Adirondack Journal of Environmental Studies, Volume 21 by Kelly Adirondack Center

ADIRONDACK RESEARCH CONSORTIUM

UNION COLLEGE

201 PAOLOZZI CENTER | PAUL SMITHâ&#x20AC;&#x2122;S COLLEGE

807 UNION STREET

P.O. BOX 96

SCHENECTADY, NEW YORK 12308

PAUL SMITHS, NEW YORK 12970

THE ADIRONDACK JOURNAL of Environmental Studies

THE KELLY ADIRONDACK CENTER

THE ADIRONDACK JOURNAL of Environmental Studies A JOURNAL OF THE ADIRONDACK RESEARCH CONSORTIUM

PUBLISHED BY THE KELLY ADIRONDACK CENTER AT UNION COLLEGE IN PARTNERSHIP WITH THE ADIRONDACK RESEARCH CONSORTIUM

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21 THE ADIRONDACK JOURNAL of Environmental Studies A JOURNAL OF THE ADIRONDACK RESEARCH CONSORTIUM

PUBLISHED BY THE KELLY ADIRONDACK CENTER AT UNION COLLEGE IN PARTNERSHIP WITH THE ADIRONDACK RESEARCH CONSORTIUM

TABLE OF CONTENTS

FOREWORD

Assemblyman Steve Englebright 1: INTRODUCTION

Bruce W. Selleck and Jeffrey R. Chiarenzelli 2: REGIONAL GEOLOGICAL SETTING OF THE ADIRONDACK MOUNTAINS, NEW YORK

James M. McLelland 3: BEDROCK GEOLOGY OF THE ADIRONDACK REGION

Jeffrey R. Chiarenzelli and Bruce W. Selleck 4: EPISODES IN GEOLOGICAL INVESTIGATIONS OF THE ADIRONDACKS

William H. Peck 5: METAMORPHIC CONDITIONS OF ADIRONDACK ROCKS

Robert S. Darling and William H. Peck 6: RARE EARTH ELEMENT AND YTTRIUM MINERAL OCCURRENCES IN THE ADIRONDACK MOUNTAINS

Marian V. Lupulescu, Jeffrey R. Chiarenzelli, and Jared Singer 7: MINING, GEOLOGY, AND GEOLOGIC HISTORY OF THE GARNETS AT THE BARTON GARNET MINE, GORE MOUNTAIN, NEW YORK

William Kelly 8: FAULTS AND FRACTURE SYSTEMS IN THE BASEMENT ROCKS OF THE ADIRONDACK MOUNTAINS, NEW YORK

101

David W. Valentino, Joshua D. Valentino, Jeffrey R. Chiarenzelli, and Richie Inclima 9: POST-VALLEY HEADS DEGLACIATION OF THE ADIRONDACK MOUNTAINS AND ADJACENT LOWLANDS

119

David A. Franzi, John C. Ridge, Donald L. Pair, David DeSimone, John A. Rayburn, and David J. Barclay 10: SOILS AND SOIL ACIDIFICATION IN THE ADIRONDACK MOUNTAINS

147

Richard April, Dianne Keller, and Michele Hluchy 11: ADIRONDACK LANDSLIDES: HISTORY, EXPOSURES, AND CLIMBING

167

Kevin B. MacKenzie

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M I S S I O N S TAT E M E N T The Adirondack Journal of Environmental Studies (AJES) exists to foster a dialogue about the broad range of issues that concern the Adirondacks and Northern Forest. AJES serves to bridge the gaps among academic disciplines and among researchers and practitioners devoted to understanding and promoting the development of sustainable communities, both human and wild. The journal purposefully avoids serving as a vehicle for any single or special point of view. To the contrary, in searching for common ground AJES welcomes variety and a broad spectrum of perspectives from its contributors.

DIKE ON WHITEFACE MOUNTAIN

THE A DI RON DACK JOURNA L OF E NV IRONME NTA L S TUDIE S

ADIRONDACK RESEARCH CONSORTIUM Finding Ways to Share Research and Information 2016 BOARD OF DIRECTORS

Daniel Spada

David Miller

PRESIDENT

TREASURER

Tupper Lake, NY

Ballston Lake, NY

Eileen Allen

Daniel Fitts

VICE PRESIDENT

SUNY Plattsburgh Center for Earth & Environmental Science

SECRETARY

Adirondack Research Consortium

Brian Chabot VICE PRESIDENT

Cornell University BOARD MEMB E R S

Hallie Bond Union College, Kelly Adirondack Center

Caleb Northrop Union College, Kelly Adirondack Center

Jeffrey Chiarenzelli St. Lawrence University

William Porter Michigan State University

Jeff Denkenberger Molpus Timberlands Management, LLC

Bruce Selleck Colgate University

Curt Gervich SUNY Plattsburgh Center for Earth & Environmental Science

Gregory Slack Clarkson University

Willie Janeway Adirondack Council Amanda Lavigne Clarkson University

Elizabeth Thorndike Cornell University Daniel Fitts EXECUTIVE DIRECTOR

Adirondack Research Consortium

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THE ARC RECOGNIZES AND THANKS OUR 2016-17 PARTNERS AND SPONSORS

LEADING PARTNER:

CONTRIBUTING PARTNERS:

AVANGRID

The Adirondack Council

SUSTAINING PARTNERS:

Brookfield Renewable Power New York State Energy Research and Development Authority Paul Smith’s College Rockefeller Institute of Government SUNY-College of Environmental Science and Forestry Union College SPONSORING PARTNERS:

Adirondack Museum Adirondack Nature Conservancy Cornell University Dept. of Natural Resources Open Space Institute The Wild Center LOCAL GOVERNMENT PARTNERS:

Adirondack Park Local Government Review Board Town of Newcomb

Ecology and Environment, Inc.

PARTNERS:

Empire State Forest Products Association

Adirondack Community College

SUPPORTING PARTNERS:

Boquet Foundation Clarkson University Colgate University National Grid St. Lawrence University SUNY Plattsburgh University of Vermont FOUNDATION SPONSORSHIP PROVIDED BY:

Adirondack Lakes Survey Corporation Adirondack Park Institute, Inc. Adirondack Wild Audubon New York International Paper’s Ticonderoga Mill ASSOCIATE PARTNERS:

Mountain Lake PBS NYS Olympic Regional Development Authority

The Walbridge Fund LTD Cloudsplitter Foundation

WITH SPECIAL THANKS TO PAUL SMITH’S

Colgate University Upstate Institute

COLLEGE FOR HOUSING THE OFFICES OF THE

Glenn and Carol Pearsall Adirondack Foundation International Paper Foundation Northern New York Audubon Cullman Foundation

THE A DI RON DACK JOURNA L OF E NV IRONME NTA L S TUDIE S

ADIRONDACK RESEARCH CONSORTIUM.

ADIRONDACK JOURNAL of ENVIRONMENTAL STUDIES EXECUTIVE EDITOR

Caleb Northrop Union College, Kelly Adirondack Center 807 Union Street, Feigenbaum Hall, Schenectady, NY 12308 northroc@union.edu ASSOCIATE EDITOR

Jeffrey Chiarenzelli St. Lawrence University, Department of Geology 23 Romoda Drive, Canton, NY 13617 jchiaren@stlawu.edu ASSOCIATE EDITOR

Bruce Selleck Colgate University, Department of Geology 13 Oak Drive, Hamilton, NY 13346 bselleck@colgate.edu

Stephen C. Ainlay, Ph.D. PRESIDENT

Union College

CONTRIBUTING TO AJES

We encourage the submission of manuscripts, reviews, photographs, artwork, and letters to the editor. For additional information please visit the AJES website at www.ajes.org. THE VIEWS EXPRESSED IN AJES ARE THE AUTHORS’ AND NOT NECESSARILY THOSE OF THE EDITOR, PUBLISHER, UNION COLLEGE, OR THE ADIRONDACK RESEARCH CONSORTIUM. ISSN: 1075-0436 ©2016

Color photos are courtesy of Kevin B. MacKenzie. Cover photo: Basin’s East Face with the McIntyre Range in the background. This special color volume of AJES was made possible by additional support from the following:

A Union College Planning and Priorities Grant The Malcolm and Sylvia Boyce Fund, Department of Geology, Colgate University. The Colgate University Upstate Institute Barton International

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FOREWORD The Adirondack Mountains are a treasured place in the Empire State. The Adirondack Park represents our best efforts as citizens to preserve nature and protect the wild part of the state from over-development. At the same time, the Adirondacks offer opportunities for respite and recreation, as well as balanced development of a resource- and tourism-based economy. They are a place where all of us can â&#x20AC;&#x2DC;get awayâ&#x20AC;&#x2122; to enjoy the outdoors, and for the scientific community, the Adirondacks are a reserve where important studies take place. This special issue of the Adirondack Journal of Environmental Studies is devoted to articles about the geological research that has been carried out within the Adirondacks, and it provides an important update for the scientific community, residents, and visitors. On behalf of my fellow New Yorkers, I thank the Adirondack Research Consortium and the Kelly Adirondack Center of Union College for their work to bring this issue to print. We will all be better-informed citizens as a result of this effort. Assemblyman Steve Englebright (D-Setauket) CHAIRMAN OF THE COMMITTEE ON ENVIRONMENTAL CONSERVATION

July 2016

TOP OF THE CRUCIFLYER SLIDE ON MT. COLDEN

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INTRODUCTION BRUCE W. SELLECK AND JEFFREY R. CHIARENZELLI

Geological study of the Adirondacks began in the 1830s with the forays of Ebenezer Emmons, under the aegis of the New York State Geological Survey. Scientific research has continued unabated, and in recent years, great strides have been made in unraveling the complexities of the plate tectonic history, bedrock geology, glacial processes, and soil/water systems. Much of this research has been spurred by economic and environmental concerns, but in the main, the Adirondacks are studied because they are fundamentally interesting, as a geological terrain set in a landscape of preserved, â&#x20AC;&#x2DC;forever wildâ&#x20AC;&#x2122; ecosystems. This issue of the Adirondack Journal of Environmental Studies gathers our current knowledge of the geology of the Adirondacks with the goal of informing a broader public audience. The papers summarize historical and current work, calling upon the accumulated studies of many excellent geoscientists who have worked in the Adirondacks for nearly two centuries. The first article in this issue, authored by James McLelland, places the Adirondacks in a regional context and reviews the plate tectonic history of the Grenville Province, that vast sweep of North American continental crust of which the Adirondacks are but a small fragment. The paper by Chiarenzelli and Selleck explores the bedrock geology of the region, which is dominated by igneous and metamorphic rocks 1.4 to 1.0 billion years of age. Also described in that article are the younger (but still quite ancient) Paleozoic rocks found in and around the Adirondack region. William Peck provides a review of the history of geological studies of the Adirondacks. Peck describes how the study of our local rocks has always been framed within the broader scientific community and how new technologies provide opportunities to answer old questions. Robert Darling and William Peck then describe how we have come to know the temperatures and pressures experienced by the metamorphic rocks of the region; fundamental knowledge that guides meaningful reconstruction of the

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plate tectonic setting of the region during the plate collision events that built the ancient mountain belt known as the Grenville Orogen. Although mining activity in currently very limited in the region, the Adirondacks were a major source of iron ore until the 1970s. Papers by Marian Lupulescu (with co-authors Chiarenzelli and Jared Singer) and William Kelly explore, respectively, the origin of rare earth element and garnet deposits in the Adirondacks. The utilization of both natural materials is increasing in today’s technological-based economy and the discovery of new and old resources of paramount importance. David Valentino, with co-authors Joshua Valentino and Jeffrey Chiarenzelli, reviews the complex array of fracture and fault systems within the Adirondacks and how those systems help to shape the rugged landscapes of our mountains. The importance of the Pleistocene glaciers and the immediate post-glacial history of the region are developed by David Franzi and co-authors (Ridge, Pair, DeSimone, Rayburn, and Barclay). Glacial erosion helped to shape the bedrock ‘skeleton’ that undergirds Adirondack topography, but sediment deposited as the glaciers receded makes up the ‘skin’ that covers much of the region. Richard April, Michele Hluchy, and Diane Keller then summarize recent work on Adirondack soils. The mineralogy and chemistry of these soil systems is of paramount importance to understanding the impact of acid precipitation and the recovery of ecosystems as acid input is reduced. Kevin MacKenzie describes modern landslides, the products of steep slopes and local soil saturation due to Hurricane Irene and numerous older precipitation events in the High Peaks region. The “slides” provide not only an unparalleled window into the geology of the High Peaks but also a cautionary note for developed areas within the park. We hope that this issue will find broad readership and urge readers to take advantage of the references provided by the authors. The Adirondacks are a gem, indeed, and appreciation of their special character is only enhanced by greater scientific understanding. Finally, we recognize and celebrate the many important contributions made by James M. McLelland, Dana Professor of Geology Emeritus, Colgate University. Jim’s work was groundbreaking, and his many publications have guided the studies of many other scientists over the last four decades. Jim also served as a gracious and generous mentor for younger geologists and continues to be a source of inspiration and new ideas. Jim, many thanks for all you have done to help us understand the Adirondacks and inspire new generations of researchers.

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REGIONAL GEOLOGICAL SETTING OF THE ADIRONDACK MOUNTAINS, NEW YORK JAMES M. MCLELLAND

Department of Geology, Colgate University, Hamilton, NY 13346, jmclelland@citlink.net

KEYWORDS:

Adirondack Highlands, Adirondack Lowlands, Grenville Province, Appalachian Inliers, Laurentia, Shawinigan Orogeny, Ottawan Orogeny

INTRODUCTION The ~180 x 150 kilometer (km) (115 x 95 mi), slightly elliptical Adirondack dome (Figure 1) is underlain by Mesoproterozoic (1600-1000 Ma) metamorphic and igneous rocks that range in age from ca. 1350 to 1040 Ma and is surrounded by flat-lying ca. 500 Ma Lower Paleozoic sedimentary rocks. As shown in Figure 1, it is divided into the Adirondack Highlands Terrane (HL) and the Adirondack Lowlands Terrane (LL) separated by a steep, northwest dipping, oblique normal fault zone known as the Carthage-Colton shear zone (CCZ). The underlying Mesoproterozoic units have undergone pronounced high temperature ductile deformation that resulted in large, upright to flat-lying folds formed during two major orogenic events: the 1210-1140 Ma Shawinigan Orogeny and the 1090-980 Ma Grenville Orogeny. The latter consists of two major pulses referred to as the Ottawan Orogeny and Rigolet Orogeny. Orogenesis was accompanied by high grade regional metamorphism ranging from upper amphibolite (pressure of ~6-7 kbar, temperature of ~600-750 Â°C) to granulite facies (pressure of ~7-8 kbar, temperature of ~800-830 Â°C) conditions. During each orogeny, strong, widespread penetrative deformation resulted in mylonite and ribbon gneiss. Both orogenies were followed by post-orogenic igneous activity, i.e.,

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a voluminous ca. 1155 Ma anorthosite-mangerite-charnockite-granite (AMCG) suite and the distinctive ca. 1050 Ma Lyon Mt. Granite that rims much of the Adirondack Highlands (shown in red on Figure 1). By ca. 550 Ma the mountain range had been eroded to sea level, deposition began, and marine sediments blanketed the area. During the Mesozoic Era (ca. 250-60 Ma), the area was vertically uplifted and exhumed by erosion to form the current topographic dome. Faulting, erosion, and glaciation further modified the present-day second generation mountain range. In this paper, I seek to relate these characteristics to the regional geology of Canada and the Appalachian Mountains. The interested reader will find a more comprehensive and in-depth presentation for material in this article as well as an extensive bibliography in McLelland, Selleck, and Bickford (2010, 2013) and references given therein. These references are provided at the end of this article. Figure 1. Generalized geological and rock type age distribution map of the Adirondack Regions. Units designated by patterns and initials consist of igneous rocks dated by U-Pb zircon geochronology with ages indicated in the legend.Units present only in the Adirondack Highlands terrane (AHT) are Royal Mountain Tonalite and Granodiorite (RMTG; southern HL only), Hawkeye Granite (HWK), Lyon Mountain Granite (LMG) and anorthosite (ANT). Units present in the Lowlands (LL) only are: Hyde School Granitic Gneiss and Rockport Granite (HSRG; Hyde School also contains tonalite), Rossie Diorite and Antwerp Granodiorite (RDAG), Hermon Granite (HERM). Granitoid members of the AMCG suite (MCG) are present in both the Highlands and Lowlands terranes. Unpatterned areas consist primarily of metasedimentary rocks, glacial cover, or undivided units. Key: Antwerp (A), Ausable Falls (AF), Black Lake Shear Zone (BLSZ), Canton (CA), Canada Lake isocline (CLI), Carthage-Colton Shear Zone (CCZ), Gouverneur (GO), Gore Mt. (GM), Lyon Mountain (LM), Lake Placid (LP), Oregon Dome (OD), Piseco antiform (P), Rossie (R), Schroon Lake (ScL), Snowy Mountain dome (SM), Ophiolite (X). This figure is modified after McLelland et al. (2010).

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RELATIONSHIP OF THE ADIRONDACKS TO THE CANADIAN GRENVILLE PROVINCE Figure 2 shows an expanded view of eastern North America, including the large Grenville Province of Canada, its Adirondack extension, and related rocks occurring in inliers in the Appalachian Mountains. The area designated by an upper-left to lower-right diagonal ruling locates basement rocks of the 1600-980 Ma Grenville Orogen buried beneath Paleozoic cover. This region is divided by a northeast-trending magnetic anomaly referred to as the New YorkAlabama lineament that was interpreted by King and Dietz (1978) as a suture marking the ca. 1250-1200 Ma collision (i.e., the Shawinigan Orogeny) of the ancestral Southern Appalachian basement with the Eastern Granite Rhyolite Province (EGR) to the northwest of the lineament. The Grenville Province has been divided into a number of subunits (Rivers 1989). The largest of these are the Allochthonous Polycyclic Belt (APB, Figure 2), the Allochthonous Monocyclic Belt (AMB, Figure 2), and the Parautochthonous Belt (PB, Figure 2). The term Allochthonous refers to the fact that these belts have been tectonically transported from the site(s) where the belt originally formed. Alternatively, autochthonous refers to belts that have remained in place at the site(s) where they originally formed. A polycyclic belt has experienced multiple major orogenies associated with the opening and closing of ocean basins over a long time interval. A monocyclic belt is one that has experienced a single major orogenic cycle. Parautochthonous belts have been tectonically displaced by relatively small distances from where they formed.

Figure 2. Generalized map depicting major tectonic and geochronological subdivisions in the eastern USA. The Grenville Province is shown in medium gray and its exposed portions are indicated by heavy outlines. Dark areas along the spine of the Appalachians are inliers of Grenville Rocks affected by Appalachian orogensis. See legend on figure for details and other symbols. The diagonally ruled area along New York-Alabama Lineament is covered portion of the Grenville Province in the eastern United States. The diagonally ruled northeast corner of the diagram is parts of the orogenic lid (i.e,. rocks relative high in the crust during Grenville deformation). Abbreviations: AD = Adirondack Mountains, EGR = Eastern Granite-Rhyolite Province, LE= Lake Erie, LO= Lake Ontario, SLR= St. Lawrence River. This figure is modified after McLelland et al. (2010).

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The APB evolved from ca. 2000 Ma to 1000 Ma as a series of successive accretive continental margin arcs and orogenies. Remnants of several of these arcs extend through the EGR. The AMB, to which the Adirondacks belong, contains only rocks in the age range 1350-1000 Ma. The AMB experienced two major orogenies and associated high temperature metamorphic events, i.e., the Shawinigan (ca. 1200-1150 Ma) and the Ottawan (1090-1020 Ma) orogenies. The latter resulted from the collision of Amazonia with eastern North America, i.e., Laurentia (Figure 3). The Rigolet Orogeny (ca. 1010-980 Ma) was the final pulse of this collision and caused thrusting of the northwestern margin of the Grenville Province over the ancient > 2500 Ma basement rocks of the Superior Province forming the Grenville Front Thrust (black teeth on Figure 2) and the Parautochthonous Belt. The Rigolet Orogeny was a relatively mild tectonothermal event and, in the Adirondacks, has few manifestations other than some narrow overgrowths on zircons. Both the Shawinigan and Ottawan orogenies resulted in pronounced crustal thickening caused by compression and thrust stacking during the collision of large blocks of continental crust. A simplified history of these orogenic events is summarized in map view in Figure 3 and in cross-section in Figure 4. Beginning at ca. 1350-1250 Ma the continental margin arc of Laurentia was rifted apart by southeastward extension producing several ca. 1350 Ma fragments that were situated in a widening seaway similar in size to the Sea of Japan. Sediments accumulated in the growing basin (Figure 3A) that would eventually evolve into the Central Metasedimentary Belt that is a major constituent of the AMB and is bordered on the west by the Central Metasedimentary Belt Tectonic Zone (CMBTZ, Figure 2). The 1350 Ma fragments were distributed throughout the basin and today are found along the western margin of the CMB near the town of Dysart, as well as, the Adirondacks, and Mt. Holly region of the Green Mts. in western Vermont. Taken together, these ca. 1350 Ma fragments are referred to as the Dysart-Mt. Holly suite. To the east of this basin lay a large block of continental crust referred to as Adirondis that had been rifted from the margin of what is now Quebec. The future locations of Vermont, New York, and New Jersey are indicated on Figure 3A. By ca. 1250-1220 Ma eastward subduction of oceanic crust had begun beneath the rifted fragments as well as Adirondis and gave rise to igneous activity and deformation referred to as the Elzevirian Orogeny (Figure 3B). By 1220-1200 Ma the western seaway closed out against Laurentia and subduction switched to a westward polarity beneath the CMB resulting in intrusions of granodiorites, diorites, and granites of the Antwerp-Rossie (RDAG) and Hermon (HERM) suites located on Figure 1 in the Adirondack Lowlands. In addition, an ophiolite complex including oceanic crust and upper mantle peridotite was emplaced in what is now the Adirondack Lowlands (Figure 3C). Similar ophiolites occur in the Central Metasedimentary Belt in Ontario.

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Figure 3. Schematic panel diagram summarizing the distribution and interaction of various segments of northeastern Laurentia during the interval 1300-1050 Ma encompassing the rifting, opening and closing of the Central Metasedimentary Belt back-arc basin (CMBB), Trans-Adirondack back-arc basin (TAB), and the Ottawan collision with Amazonia. Note that prior to ca. 1300 Ma subduction had been to the northwest beneath the Laurentian margin. Blocky black arrows indicate polarity of subduction. Different shades of gray identify important terranes and arcs. Blocky white arrows represent extension. The crustal block labeled Adirondis is a large Eâ&#x20AC;&#x201C;W crustal fragment rifted from Laurentia at ca. 1400-1300 Ma and by collision at ca. 1200-1000 Ma. Vermont (VT), New York (NY), and New Jersey (NJ). Amazonia is inferred to remain south of the Adirondis region until ca. 1090 Ma, The Pyrites Ophiolite Complex is represented by the small black region in the CMB. Abbreviations: AM = Amazonia, AMCG = anorthosite-mangerite-charnockite-granite suite, AT = Atikonak River Anorthosite, FGF = future Grenville Front, LSJ = Lac St. Jean Anorthosite, MA = Marcy anorthosite. This figure is modified after McLelland et al. (2010).

By ca. 1200-1160 Ma subduction beneath the eastern margin of the AMB closed out the eastern seaway and resulted in the powerful Shawinigan Orogeny, including the intrusion of the Hyde School and Rockport synorogenic granites (HSRG on Figure 1). During this collision rocks of the Lowlands were thrust eastward over the Adirondack Highlands for a large but unknown distance, and Adirondis became welded to Laurentia (Figure 3D). The Shawinigan collisions greatly increased the thickness of the crust and lithosphere and by ca. 1155 Ma delamination set in, and the crustal and lithospheric mantle root foundered, then sank, into the hot, ductile mantle. The foundered material was replaced by juvenile asthenosphere that underwent melting to produce gabbroic magma. The gabbroic melts crystallized plagioclase that floated in the dense, high pressure gabbroic magma and formed rafts of plagioclase-rich anorthosite with individual grains of andesine reaching 0.25 m or more in size. Simultaneously, magmatic and mantle heat caused melting of the granitoid VOLUME 21

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material of the lower crust to produce compositions ranging from mafic syenite, monzonite, and granite and further weakened the crust. Ultimately, the gabbros and their anorthositic cumulates ascended along zones of weakness and were emplaced in the mid- to upper-crust to form the ca. 1155 Ma AMCG suites, e.g., Marcy and Oregon Dome (OD) massifs, Morin (M) massif, Lac St. Jean (LSJ) complex, and perhaps the Atikonak (AT) massif (Figure 3E). During all of the preceding orogenic activity, oceanic crust between North America and Amazonia had been closing out via subduction beneath the latter. Closure came at ca. 1090-1050 Ma when the collision between the two finally took place and resulted in the powerful Ottawan Orogeny that produced the Allochthon Boundary Thrust (open teeth on Figure 2), great crustal thickening, widespread ductile deformation, etc. Within the Adirondack Highlands granulite facies temperatures of 750-810 °C and pressures of 6-8 kbar were attained and titanite cooling ages of ca. 1030 Ma are common. By contrast, the Adirondack Lowlands record titanite and hornblende cooling ages greater than ca 1060 Ma reflecting temperatures that the Lowlands did not exceed experience temperatures exceeding ~500 °C during the Ottawan Orogeny. This otherwise enigmatic result can be explained by the fact that, during the Ottawan Orogeny, the Lowlands was situated on top of the Highlands as an orogenic lid; an area higher in the crust above the main zone of ductile deformation. At the end of the Ottawan, during orogenic collapse, the Lowlands (LL) was dropped down along the CCZ (Figure 1) into juxtaposition with the Highlands (HL). Here we note that much of the AMB was situated within the orogenic lid during the Ottawan Orogeny. It is due to this insulation that sedimentary units are so well preserved in the AMB and led to its title of the Central Metasedimentary Belt (CMB, Figure 2) within which greenschist facies assemblages are common. Another orogenic lid is present in the far northeastern reaches of the Grenville Province (diagonal ruling in the top right corner of Figure 2). Due to the inaccessibility of the region its contents and boundaries are not well known, but its existence is certain. By 1090 Ma southeastward subduction beneath the northwestern margin of Laurentia (Figure 3F) eventuated in the closure of the ocean basin and a powerful head-on collision between Amazonia and southeastern Laurentia that resulted in the Ottawan and Rigolet orogenies. It was at this time that the Allochthon Boundary Thrust (ABT) drove great wedges of southeast-dipping metamorphic rocks to the northwest producing the APB. The thrusting was accompanied by very high temperatures in the deep crust, which became very ductile and flowed to produce large, tight folds with overall sub-horizontal attitudes. These structures are referred to as nappes and are characteristic of hot, longlived orogens. One of these structures is shown in Figure 1 where its western portion in the southern Adirondacks is represented by a “bent index finger” outcrop pattern. This nappe structure extends ~100 km east to Saratoga Springs where it disappears beneath young cover rocks. Other folds in the Adirondacks are of similar dimensions and rival structures in the Himalayas and Alps. In terms of its extent (i.e., world-wide) and the metamorphic conditions attained, the Ottawan Orogeny was a world-class mountain building event.

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Figure 4 presents a cross-sectional summary of the events discussed above. The rifted fragments of the Dysart-Mt. Holly suite are shown just after ca. 1300 Ma together with the Elzevirian (E) arc and southeastern Adirondis marginal arc separated by the CMB and Trans-Adirondack Basin (TAB). The AHT and Green Mountains are shown along the eastern margin of Adirondis. By ca. 1200 Ma (Figure 4B) the CMB basin closed out against the Central Gneiss Belt (CGB) producing the Central Metasedimentary Belt Boundary Zone Thrust (CMBBZ) and constituting an early phase of the Shawinigan Orogeny. To the east, ophiolites were obducted onto the Adirondack Lowlands Terrane (ALT) and subduction driven magmatism ceased in the Adirondack Highlands Terrane and Green Mountains Terrane (AHT-GMT). By ca. 1120 Ma the Shawinigan Orogeny was fully developed, and the TAB closed out resulting in the collision of the CMB-ALT terrane with the AHT. Importantly, the CMB-ALT terrane was thrust eastward over the AHT for an unspecified and unknown distance. Strong high temperature deformation resulted in large, flat-lying ductile nappes. The nappes are labelled F1 in order to differentiate them from later Ottawan nappes labelled F2 (Figure 4F). Figure 4D depicts the delamination of the over thickened Shawinigan crust and lithosphere and consequent orogen collapse together with ascent of hot asthenosphere and the formation of AMCG magmatism.

Figure 4. Plate tectonic models showing proposed tectonic evolution along a line from the Adirondack Mountains to the Central Metasedimentary Belt Boundary Zone (CMBBZ). The green areas schematically represent the Dysart-Mt. Holly suite (DAMH). Abbreviations: AHT =Adirondack Highlands terrane, AHTGMT = Adirondack Highlands-Green Mountains terrane, ALT = Adirondack Lowlands terrane, AMCG = anorthosite-monzonite-charnockite-granite suite, BSZ = Bancroft shear zone, CCZ = Carthage-Colton shear zone, CGB = Central gneiss belt, CMB = Central metasedimentary belt, E = Elzevir Terrane, EASZ = Eastern Adirondack shear zone, F = Frontenac terrane, HSG = Hyde School , MSZ = Maberly Shear Zone, OPH = Pyrite Ophiolite Complex, RLSZ = Robertson Lake Shear Zone, TAB = Trans-Adirondack basin. The eastern Adirondack extensional shear zone is shown by the heavy fault line and arrow in the bottom (1050 Ma) panel. This figure is modified after McLelland et al. (2010). VOLUME 21

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Figure 4E is hypothetical and represents an attempt to account for a group of intrusive rocks referred to as the Hawkeye Granite suite that yield ages between ca. 1100 Ma and 1090 Ma. However, these ages were determined in the mid-1980â&#x20AC;&#x2122;s when geochronological techniques allowed for less precision. The ages may well be hybrid and result from the incorporation of both igneous cores and metamorphic overgrowths. Zircon, the mineral used for dating, has been shown to retain its isotopic systematics throughout high-grade metamorphism but often also can grow new metamorphic rims on igneous cores. The age of the Hawkeye Granite suite is regarded as conjectural until additional data is collected. Figure 4F depicts the collision of Laurentia with Amazonia and the onset of the Ottawan Orogeny with its very high grade metamorphism and ductile deformation. The figure emphasizes the northwest-directed thrusting and the large northwest directed F2 nappes with subhorizontal attitudes typical of major metamorphism in large, hot orogens associated with major continental collisions. The actual suture between Laurentia and Amazonia is not exposed and may lie buried beneath younger rocks in the Appalachians. In Figure 4G the Adirondack region has collapsed and the ALT down faulted to the west along the Carthage-Colton (CCZ) an oblique normal fault. A mirror image of the CCZ has been found in the easternmost Adirondacks where Highland rocks have been down faulted to the east. This major structure is referred to as the Eastern Adirondack Shear Zone (EASZ). Accompanying the down faulting was the emplacement of large volumes of the Lyon Mountain Granite.

RELATIONSHIP OF THE ADIRONDACKS TO APPALACHIAN GRENVILLE INLIERS In Figure 2, the major occurrences of Proterozoic basement inliers in the Appalachians are shown in black. In most cases, these bodies, which are relatively resistant to erosion, form the upper elevations of the Appalachian mountain belt. There is remarkable continuity of Adirondack geology with that exposed within the Appalachian Proterozoic massifs. Thus, in the case of the Mt. Holly complex of Vermont Green Mountains, the ca. 1350 Ma tonalitic rocks of the Dysart-Mt. Holly complex are well represented and metasedimentary units are the same as those in the eastern Adirondack Highlands. However, the ca. 1050 Ma Lyon Mt. Granite and evidence of Ottawan metamorphism are sparse to absent in Vermont suggesting that the Mt. Holly rocks may have been part of the orogenic lid that sat on top of the Adirondack Highlands from ca. 1160-1050 Ma, similar to the Adirondack Lowlands. This possibility is under investigation. The ca. 1350 Ma Dysart-Mt. Holly suite is present in the northern Appalachian inliers and southward through the New Jersey Highlands and ca. 1250 Ma Elzevirian rocks occur as far south as the Baltimore Gneiss Domes. Granitic rocks of ca. 1172 Ma Shawinigan age, common in the Adirondack Lowlands, are present within the Mt. Holly complex. In Massachusetts, 35% of the Berkshire massif is underlain by the ca. 1179 Ma Tyringham granitic gneiss that intrudes metasedimentary

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gneisses similar to those in the AHT, Green Mountains, and Hudson Highlands. In the Hudson Highlands, the widespread Storm King granite has been dated at ca. 1174 Ma and was intruded by the ca. 1140-1130 Ma Canopus and Brewster plutons. Within the New Jersey Highlands, the Byram-Hopatcong pluton has been dated at ca. 1176 Ma. These ages indicate that Shawinigan magmatism extended well to the south of the Adirondacks and was followed by granitic magmatism of AMCG age. Some small occurrences of layers of anorthositic rock within the granitoids suggest that the full AMCG is present, and this possibility is reinforced by the presence of an Adirondack-type anorthosite in the Honeybrook Uplands of Pennsylvania. Consistent with this is clear evidence for the presence of strong Shawinigan deformation and metamorphism at ca. 1180 Ma throughout the northeastern Appalachian inliers including New Jersey. The deformation and metamorphism has been attributed to the closure of the Trans-Adirondack Basin against Laurentia followed by ca. 1176 Ma Shawinigan magmatism and later by ca. 1040 Ma AMCG magmatism. Farther to the south, the Shenandoah massif of the Blue Ridge Mountains (Figure 2) extends through most of the State of Virginia. It contains a large volume of igneous rocks ranging in age from ca. 1185-1165 Ma that correspond to Shawinigan magmatism in the Adirondacks. They were followed by granitic magmatism at ca. 1153-1143 Ma including small volumes of anorthosite and are correlated with the Adirondack AMCG suite. Also present are granitic rocks dated at ca. 1050-1030 Ma that correspond to the Lyon Mt. Granite of the Adirondacks. The Shenandoah massif shows some evidence of metamorphism and deformation at ca. 11551144 Ma, but evidence of widespread, high grade metamorphism is not plentiful. However, within the Smoky Mountains of the French Broad Massif to the south in Tennessee (Figure 2), leucosomes in migmatites have been dated at ca. 1194 Ma and granitoid plutons yield ages of 1167 Ga, both of Shawinigan age. At Mt. Rogers near the north end of the French Broad Massif there are ca. 1174-1161 Ma plutons that were intruded into very hot (ca. 750 Â°C) upper amphibolite facies crust. These events reflect Shawinigan magmatism and high grade metamorphism. Given this, it is suggested here that it is just a matter of time before similar evidence for Shawinigan metamorphism is described from the Shenandoah massif. Both the Shenandoah and French Broad massifs contain ample evidence for ca. 1050 Ma Ottawan magmatism and metamorphism similar to the Adirondack Highlands. The ca. 1050 Ma leucogranites in all these regions are generally only mildly deformed suggesting that they, like the Lyon Mt. Granite, were emplaced late in the Ottawan Orogeny and are interpreted as late-tectonic intrusions associated with the extensional collapse of the Ottawan orogen. Within the Pine Mountain window in Alabama and Georgia (Figure 2), intrusive rocks ranging in age from ca. 1060 to 1010 Ma and contain xenoliths ranging in age from ca. 1140 to 1020 Ma. Similarly, the 1050 Ma State Farm Gneiss and Montpelier anorthosite of the Goochland terrane in eastern Virignia (Figure 2) correspond to the Lyon Mt. Granite and the late- to post-Ottawan anorthosites of the CRUML-type (Chateau-Richer, St. Urbain, Matawa, Labrieville) AMCG suite in western Quebec and ca. 1045 Ma Roseland anorthosite of the northern Shenandoah massif. Like the post- to late-Shawinigan AMCG suite, the ca. 1050 Ma examples of AMCG magmatism are associated with the collapse of large orogens.

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Notwithstanding the similarities between the Adirondacks and the Mesoproterozoic inliers of the Appalachians, there are some significant differences. The first of these is that the Adirondacks and the Canadian Grenville Province underwent orthogonal collision with Amazonia (Figure 4) and experienced maximum compressional strain. In contrast, the Appalachian region underwent a lower angle, oblique collision with Amazonia and contractional strain was less than farther north. In addition, lead isotope data indicates that the Canadian Grenville Province, including the Adirondacks, were derived from North American crust, whereas the southern and central Appalachian Mesoproterozoic massifs were derived from crust that was probably part of Amazonia until ca. 1200 Ma and was transferred to North America during continental collision.

SUMMARY AND CONCLUSIONS The Adirondacks are clearly part of the Grenville Province of Canada equivalent to rocks in the CMB and the AMB (Figure 2). They experienced both the Shawinigan and Ottawan orogenies as well as intrusion of the ca. 1150 Ma AMCG suite that characterize the Grenville Province. The oldest rocks in the Adirondacks are the ca. 1350 Ma tonalites of the Dysart-Mt. Holly suite that was rifted from the Andean-type continental margin of Mesoproterozoic Canada. In addition to the above, lead isotope studies demonstrate that the Adirondacks as well as the Canadian Grenville Province evolved from North American basement rocks that extend to the southwest all the way to west Texas. In contrast to this, the Mesoproterozoic inliers of the Appalachians exhibit a non-North American lead isotope signature and are thought to have been transferred from Amazonia during its ca. 1250 collision with eastern North America. Aside from this fundamental difference, the Adirondacks and Appalachian inliers share a common history of Shawinigan and Ottawan tectonic events and igneous activity, although there is a paucity of ca. 1155 Ma anorthosite plutons. Perceiving the eastern USA in the foregoing manner provides a unifying framework for understanding the evolution of this large region and is critical to our understanding of the Adirondack portion of it. L I T E R AT U R E C I T E D

McLelland, J., B. Selleck, and M.E. Bickford. 2010. “Review of the Proterozoic evolution of the Grenville Province, its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians,” in R.P. Tollo, M.J. Bartholomew, J.P. Hibbard, and P.M. Karabinos, (Eds.). From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region, Geological Society of America Memoir, 206: 21-49. McLelland, J., B. Selleck, and M.E. Bickford. 2013. “Tectonic evolution of the Adirondack Mountains and Grenville inliers within the USA,” Geoscience Canada, 40: 318-333.

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BEDROCK GEOLOGY OF THE ADIRONDACK REGION JEFFREY R. CHIARENZELLI 1 AND BRUCE W. SELLECK 2

1. Department of Geology, St. Lawrence University, Canton, NY 13617, jchiaren@stlawu.edu 2. Department of Geology, Colgate University, Hamilton, NY 13346, bselleck@colgate.edu

KEYWORDS:

Adirondacks, Tectonics, Rodinia, Paleozoic Inliers, Timeline

ABSTRACT Precambrian rocks of Adirondack Region were part of a global system of mountains whose formation approximately one billion years ago led to the assembly of a supercontinent called Rodinia. In New York State, the eroded remnants of these enormous mountains extend beneath the Paleozoic cover rocks on the edge of the Adirondack topographic dome to form the basement rocks of New York State and connect, through exposures in the Thousand Islands Region, to the bulk of the contiguous Grenville Province of the Canadian Shield. Similar rocks are exposed in basement windows along the spine of the much younger Appalachian Mountains and can be traced into Mexico and beyond. Like other areas in the Grenville Province, the High Peaks region of New York is underlain by a large intrusive body of massif anorthosite, a rock composed of exceptionally large crystals of plagioclase feldspar. Rocks in the Adirondacks range in age from approximately 1350 to 1000 million years old and record as many as three or four tectonic events which were part of the Grenville Orogenic Cycle. The net results of these events were high-grade metamorphism, strong deformation, and the widespread overprinting of original relationships and primary textural features. Younger Paleozoic rocks include Cambrian and Ordovician sandstones, limestones, and shales deposited on the eroded metamorphic and igneous basement. These sedimentary rocks are found in fault-bounded outliers within the Adirondack massif and around the Adirondack margins.

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The current topography of the Adirondacks is related to doming which began about 180 million years ago, when the Atlantic Ocean opened; although the reason(s) for this doming remain to be fully elucidated. Doming has stripped away the younger Paleozoic rocks and exposed the roots of the mountains, which at one time were deformed and metamorphosed deep in the crust.

INTRODUCTION The Precambrian rocks exposed in the Adirondack Mountains range in age between ca. 1350-1000 million years old. They are a small part of a vast area on the southeastern edge of the Canadian Shield which is known as the Grenville Structural Province (Figures 1 and 2). Rocks in the Grenville Province share a SW-NE structural grain and a complicated tectonic history which ultimately led to the assembly of supercontinent Rodinia (Figure 3). Similar in many respects to the much younger Pangea, Rodinia included all the Earthâ&#x20AC;&#x2122;s continents which were joined together by a global system of broadly synchronous mountain belts marking areas of continental convergence and eventual collision (Hoffman 1991). Figure 1: A.) Satellite photographs showing the location of the Grenville Province (purple shading). White dashed line separates exposed from covered areas. Red star lies on the Adirondack Region. B.) Terrane map of the southern Grenville Province (GP). The GP is divided into the Central Gneiss Belt (pink), the Central Granulite Terrane (grey), and the Central Metasedimentary Belt (blue). Subdivisions include the Adirondack Highlands (AH), Adirondack Lowlands (AL), Frontenac Terrane (FT), Grimsthorpe Domain (GD), Parry Sound Domain (PSD), the Southern Adirondack Terrane (SAT), and others not shown. The Appalachian Orogen and lower Paleozoic cratonic cover is stippled. C.) Location of the southern GP in the context of eastern North America. Grenville inliers in the Appalachian Mountains are shown in orange. The Grenville Front Tectonic Zone (GFTZ) separates the Archean Superior Province from rocks deformed by the Grenville Orogeny. The colored base, corresponds to rock age (Barton et al. 2003). Major population centers are shown for geographic context.

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The hallmarks of the Grenville Province include widespread deformation and metamorphic overprint that occurred during a series of events between ca. 1250-1000 million years ago, known as the Grenville Orogenic Cycle (McLelland et al. 1996; Moore and Thompson 1980). This deformation occurred deep within the crust and resulted in the addition of large amounts of new crust onto the margin of ancestral North America (i.e., Laurentia) more than a billion years ago. These crustal elements included tectonic features such as those observed today: island arcs, back-arc basins, continental arcs, continental and oceanic fragments, and intervening sedimentary basins. Deformation associated with the Grenville Province extended into the eastern margin of Laurentia where older crust of the adjacent provinces extends into, and is strongly reworked within, the Grenville Province. The Grenville Front separates rocks of the Superior Province last deformed in the Neoarchean from those affected by the Grenville event to the southeast. The tectonic history and evolution of the Grenville Province is similar to that of the Appalachian Mountains in many respects, but Grenville mountain building represents a much older and distinct series of events (Figure 4). Similar to the timespan of the Appalachian Orogeny, Grenville orogenic or mountain building events occurred over a 250 million year period. In addition, four distinct events have been recognized in the Grenville Orogenic Cycle including the Elzevirian (1245-1220 Ma), Shawinigan (1200-1150 Ma), and Grenvillian (Ottawan Phase â&#x20AC;&#x201C; 1090-1020 and Rigolet Phase â&#x20AC;&#x201C; 1000-980 Ma) orogenies (Rivers 2008). This is comparable to the series of events (Taconic, Acadian, and Alleghanian orogenies) that shaped the Appalachians. Note that rocks of the Grenville Province, which form the basement in southeastern New York in the Hudson Highlands portion of the Reading Prong and are located on the edge of North America, have been affected by both Grenville and Appalachian tectonic events. Because of the great age of the Grenville mountains, they have long since been worn down to sea level, been covered with Paleozoic sedimentary rocks, and the sediment derived from them transported to sedimentary basins in distant locations (Rainbird et al. 1997). The Adirondack Region is unique among much of the Grenville Province displaying uplift, seismic activity, and neotectonism that continues to this day (Isachsen 1981). The end result is that rocks once buried as much as 30 km in the crust are now exposed in a topographic dome elevated 1.6 km above sea level. An important part of the geologic history, which will not be fully addressed here, is how this enormous mountain range was eventually worn down to sea level. Recent studies have documented some of the major structures (normal faults) that operated when tectonic convergence ceased and the entire mountain range began to collapse under its own weight (Selleck et al. 2005).

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Figure 2: Major rock types of Adirondack Region. Major rock types and their respective ages are shown by colors indicated in the legend. Abbreviations: AH - Adirondack Highlands; AL - Adirondack Lowlands; AR - Antwerp Rossie Suite; CCSZ - Carthage-Colton Shear Zone; GSG - Grenville Supergroup; HG - Hermon Granitic Gneiss; HSG - Hyde School Gneiss; HWK - Hawkeye Granite; LMG - Lyon Mountain Granite; PLG - Piseco Lake Gneisses; and SAT - Southern Adirondack Tonalite Suite.

A TIMELINE OF OROGENIC EVOLUTION In this contribution, we will focus on the geologic events that resulted in the rocks we see exposed at the surface in the Adirondack Region today. Adirondack rocks share many similarities to those exposed in the Grenville Province of adjacent parts of Ontario and Quebec, and studies of these regions have provided us with the context for our own area. Here we will step through time from the oldest to youngest events using an approximate 50 million year interval to explain the evolution of adjacent parts of the Grenville Province and Adirondack Region (see Figure 5). The 50 million year interval is convenient as it allows discrete events to be discussed in their proper sequence and approximate duration. Note that this discussion would not be possible without the application of modern geological tools to the rocks in question. The extensive development and use of mineral geochronometers, primarily zircon and monazite, provide the critical temporal dimension to our understanding of the regionâ&#x20AC;&#x2122;s history (McLelland et al. 1988). Also note that the Adirondacks are a small portion of the Grenville Province in the approximate center of the orogenic belt that developed over a billion years ago. The scale of plate tectonics is often global, and events vary from place to place. Hence, we often have to rely on what we know about other areas and analogy to younger orogenic belts to provide the context for our discussion here.

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Figure 3: Paleoreconstruction of Rodinia at about 900 million years ago after Hoffman (1991). Precambrian cratons are shown in green, while the rocks affected by the Grenville Orogenic Cycle are shown in purple. The red star shows location of the Adirondack Region in the center of one segment of the orogen.

1350-1300 MILLION YEARS AGOâ&#x20AC;&#x201D;SUBDUCTION ALONG THE SE MARGIN OF LAURENTIA AND DEVELOPMENT OF A CONTINENTAL ARC(S) The oldest rocks exposed in the Adirondacks occur in the southern and eastern portions of the Adirondack dome (Figure 2). They consist of several strongly deformed belts of tonalitic gneisses, interlayered with younger rocks, which have yielded crystallization ages between 1350-1300 million years ago (McLelland and Chiarenzelli 1990). Their chemical composition, petrography, and other characteristics suggest they formed as part of a continental arc that rimmed the southeast margin of Laurentia (present coordinates). Continental arcs, such as the modern day Andes and the Mesozoic Sierra Nevada batholith, form incrementally as magma related to subduction beneath a continental margin emplaced in the overlying continental crust. Over time, individual batches of magma (i.e., plutons) derived from the subducting slab can amalgamate and form a batholith of truly immense proportions. The tonalitic rocks of the southern and eastern Adirondacks are similar in age and chemistry to tonalitic rocks exposed in the Green Mountains of Vermont, the Reading Prong, and in parts of Ontario and Quebec. This has led numerous workers to suggest that a large continental arc or arcs were built on the margin of Laurentia during the period between 1350-1300 million years (Rivers and Corrigan 2000). This was likely the direct result of

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the northward subduction of ocean crust beneath Laurentia. However, these tonalitic arc fragments are now widely dispersed and separated by intervening rocks of younger age (Moretton and Dickin 2013). Thus, it appears likely that some of these rocks have traveled far from their place of origin on the margin of Laurentia and have been fully incorporated into the tectonism that followed. Figure 4: A timeline showing the metamorphic and intrusive events in the Adirondack Highlands and Lowlands. The events noted by labels on the left between dashed lines are shown schematically in Figure 5.

1300-1250 MILLION YEARS AGO â&#x20AC;&#x201C; RIFTING, DEVELOPMENT OF BACKARC BASINS, AND DEPOSITION OF THE GRENVILLE SUPERGROUP In order for rocks originally developed on the margin of Laurentia to be widely dispersed and now occur far outboard from where they developed, they must have moved laterally over great distances. One way to facilitate such movement is by the opening of a rift. Much of eastern Africa is currently splitting apart; the edge of Laurentia is believed to have begun splitting apart at ca. 1300 million years ago (Dickin and McNutt 2007). This rifting allowed the dismemberment and movement of tectonic elements from the margin of Laurentia, including the tonalitic arc rocks noted above. If rifting continues, a mature ocean can

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develop, much the same as the Atlantic did when North and South America split apart from Europe and Africa after the formation of Pangea. However, because much of the Grenville Province shares a very similar sequence of metamorphosed sedimentary rocks, known as the Grenville Supergroup, it is unlikely that a full-scale ocean developed and rifting and spreading eventually slowed and stopped. A more likely possibility, which would allow the limited transportation of dismembered fragments of the tonalitic continental arc once located on the margin of Laurentia, is the opening of a back arc basin. This would allow once continuous pieces of older crust to be widely dispersed and separated by younger rocks that formed in the intervening basins. Back arc basins, like the Sea of Japan, develop when high heat flow and magma beneath an arc leads to the development of a spreading center. As happened along the coast of Asia, spreading can split apart a portion of the former continental margin (i.e., Japan), and the subduction zone â&#x20AC;&#x153;stepsâ&#x20AC;? outward away from the newly created continental margin. Although back-arc basins are not as large, or long-lived, as true oceans, they can be as much as 1000 km or more across and serve as a depocenter from thick accumulations of volcanic rocks and sediment. Eventually, they flood with sea water and develop an active volcanic spreading center, which begins to create oceanic crust. In addition, as they open, pre-existing continuous tectonic elements drift slowly away from each other and occupy locations on both sides of an opening sea or ocean. It should be emphasized that the Adirondack Region is a small piece of the greater Grenville Province (McLelland et al. 1996), and much variation can be expected along its length; however, workers have suggested that much of the southeastern coast of Laurentia was rimmed by back-arc basins at this time (Rivers and Corrigan 2000). Evidence for the development of one or more back arc basins in the Grenville Province includes volcanic and sedimentary rocks of the appropriate type and, more importantly as indicators of this environment, slivers of oceanic crust produced during their life span. Rocks called ophiolites are tectonic fragments of oceanic crust, often including thin slivers of the underlying mantle, that get thrust up (i.e., obducted) into rising mountain ranges. Such rocks are found up and down the spine of the Appalachian Mountains and in many mountain belts around the world. Recently, such rocks have been identified in the Adirondacks (Chiarenzelli et al. 2011) and in the Grenville Province of Ontario (Smith and Harris 1996). Because these two basins are separated by an intervening older fragment of crust known as the Frontenac Terrane, it has been suggested that a series of back-arc basins were operative at this time off the coast of Laurentia (Chiarenzelli et al. 2015). They provide indisputable proof that small basins with spreading centers produced oceanic crust between 1300-1250 million years ago. It was in these basins that sedimentary rocks of the Grenville Supergroup were deposited. The hallmark of the Grenville Supergroup (GSG) is a thick sequence(s) of metamorphosed carbonate rocks, such as marble and calc-silicate gneisses. These rocks generally form in warm climatic regions where the production of carbonate detritus greatly exceeds that of

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clastic sediment delivered to the depositional basin. Even more telling, in terms of the paleoclimate conditions during its deposition, is the occurrence of thick evaporitic deposits found in some portions of the GSG (de Lorraine 2001). Rocks containing evaporitic minerals like gypsum, anhydrite, or halite require evaporation rates well in excess of precipitation amounts and, generally, restriction from the open ocean. Sand-sized grains of the mineral zircon (ZrSiO4), an important geochronometer, separated from clastic units with the Grenville Supergroup in the Adirondacks suggest it was deposited between 1300-1250 million years ago (Chiarenzelli et al. 2015) within a back-arc basin that extended from the margin of Laurentia to a rifted arc fragment off the coast. This time fits well with the known depositional age of similar GSG rocks in other areas of the Grenville Province. Furthermore, it suggests that in addition to providing valuable information on the conditions at the Earth’s surface when these rocks were deposited, they have been affected by all of the subsequent orogenic events that comprise the Grenville Orogenic Cycle. From an economic standpoint, rocks of the GSG in New York, primarily near Balmat in the Adirondack Lowlands, serve as an exploitable resource of zinc, talc, marble, as well as, other resources (de Lorraine 2001).

1250-1200 MILLION YEARS AGO – INITIAL CONVERGENCE, DOCKING OF AN ARC, AND THE ELZEVIRIAN OROGENY Plutonic rocks, deformation, and metamorphism associated with an orogenic event thought to be of relatively small areal extent occurred between 1245-1220 Ma in the Grenville Province in Ontario. At this point in time, the back-arc basin in Ontario, the Central Metasedimentary Belt (Figure 2), began to collapse and rocks on the margin of Laurentia were thrust northwestward towards the Superior Province. The cause of this tectonic activity, known as the Elzevirian Orogeny, is believed to be the docking of an arc fragment, previously rifted away, back on to the margin of Laurentia (Carr et al. 2000). Our knowledge of the Elzevirian Orogeny, including its ultimate spatial extent, is incomplete. This is largely because the rocks affected by it have been profoundly impacted by later orogenic events, which may have partially or completely obliterated or overprinted features related to the Elzevirian Orogeny. Essentially, it becomes an issue of trying to “see” through younger events which strongly affected the rocks in the area. Whether or not the Elzevirian Orogeny impacted the Adirondack Region is not known for sure. However, some field evidence suggests that the rocks of the Grenville Supergroup deposited within a back-arc basin between 1300-1250 Ma underwent deformation and isoclinal folding prior to 1200 million years ago. This would make this deformation older than the recognized initiation of the Shawinigan Orogeny at 1200 million years ago. This evidence is best seen in the Adirondack Lowlands, which were spared some of the later stages of orogenesis due to their eventual location higher in the crust.

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1200-1150 MILLION YEARS AGO – CONTINENTAL COLLISION, THE SHAWINIGAN OROGENY, AND AMCG SUITE The Shawinigan Orogeny was first recognized by Corrigan (1995) and may be the most important in terms of regional metamorphism and structure in the southern Grenville Province. It is also associated with a magmatic event of immense proportions, which included the intrusion of the Marcy anorthosite massif of the High Peaks and several other even larger massifs elsewhere in the Grenville Province. Massif anorthosites are enigmatic igneous rocks and the details of their origins are still under debate. We know that they are largely restricted to the Grenville Province, are mostly restricted to the Proterozoic Era (mostly Mesoproterozoic), and are associated a distinct suite of high temperature “felsic or granitic” igneous rocks collectively known as the AMCG suite (anorthosite-mangerite-charnockitegranite suite). Until the recognition of the Shawinigan Orogeny, the AMCG suite was largely thought to be unassociated with orogenic activity (i.e., anorogenic) but are now known to have been intruded just prior (1165-1155 Ma) to the cessation of Shawinigan tectonic activity. At least in the Adirondacks, and perhaps elsewhere in the Grenville Province, the Shawinigan Orogeny set the stage for the intrusion of massif anorthosite. The Shawinigan Orogeny is thought to represent the initial collision of a large continent with Laurentia. Based on a variety of lines of evidence (Stein et al. 2014), the most likely candidate is the Precambrian core of South America, Amazonia. All the tectonic elements in between the two continents underwent extreme deformation and shortening, and accompanying metamorphism. In the Adirondack Lowlands, the Shawinigan Orogeny was the last event to affect the region, so we can get a sense of its structural style and metamorphic conditions. In general, the Lowlands show thrusting and folding towards the southeast imparting a strong SW-NE structural grain during the period 1180-1160 million years ago (Heumann et al 2006). The metamorphic grade was upper amphibolite facies and corresponded to temperatures in excess of ~660 oC, which enabled partial melting of some metasedimentary rocks of the Grenville Supergroup. Prior to, and during, deformation a number of igneous rock suites were intruded into the deformed metasedimentary rocks of the Lowlands (Peck et al. 2013). These include rocks that range in age from 1200 to 1155 million years ago. They represent renewed arc plutonism (Antwerp-Rossie Suite – ca. 1200 Ma), which gradually transitioned into the AMCG suite (Pope Mill mafic syenite – ca. 1155 Ma). In the Highlands, similarly-aged (ca. 1200-1170 Ma) rocks of arc chemistry are found within the Piseco Lake Shear Zone, which separates the central and southern Adirondacks (Gates et al. 2004). From 1165-1155 Ma enormous quantities of anorthosite and associated felsic or granitic members of the AMCG were intruded into the Adirondack Highlands (McLelland et al. 2010b). These rocks occur largely as strongly deformed, E-W arching belts of rock interleaved or interfolded with strongly deformed and attenuated metasedimentary keels.

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The structural architecture of the Adirondack Highlands is dominated by these E-W trending belts of strongly deformed rock. In addition, they often contain a shallowly plunging mineral lineation, parallel to the overall trend of the lithologic units. Within the Piseco Lake Shear Zone, a broad region (>30 km) of strongly deformed, megacrystic granitic gneisses, this lineation often becomes the dominant fabric element in the rock. So called L-tectonites with shallow lineations are the hallmark of transpressional deformation (Valentino et al. 2008), where two crustal blocks converge but also have a component of strike-slip motion as they slide past one another. In this case, structures in the rock used to decipher the relative sense of movement indicate a left-lateral displacement (Valentino et al. 2008), much as if you viewed the side of a stack playing cards lying on a table while moving them to your left. However, in this case, the playing cards are embedded in the Earth vertically. U-Pb zircon ages indicate that the movement along this shear zone and across the Central Adirondacks, in general, occurred at high-grade metamorphic conditions near the end of the Shawinigan Orogeny (ca. 1160). Sporadic development of lower-grade minerals like chlorite and muscovite also aligned with the dominant fabric may indicate movement occurred later or continued at lower grade conditions as well (Valentino et al. 2008). The proximal cause for Shawinigan deformation appears to be collision of the Southern Adirondack tonalitic arc fragment and collapse of the back-arc basin to the north. However, outboard of the Adirondacks, to the south, Amazonia may have already been converging towards, or sliding along, Laurentia (Stein et al. 2014), much the same as India is impinged on southern Asia trapping, deforming, and uplifting everything in between for the last 60 million years. Examination of the geological map of the Adirondacks presents a paradox in that the large Marcy Anorthosite appears to punch through the E-W belts of strongly deformed rock and thus post-date deformation. However, this may be more apparent than real, as the large block of relatively homogeneous anorthosite crystallizes at very high temperatures (near 1100 oC) and thus is very strong and rigid even at highgrade metamorphic conditions experienced in the Highlands, whose peak temperature was about 800 oC. Thus, the anorthosite is considered to have been intruded late in the Shawinigan deformational sequence (McLelland et al. 2010a), but probably not afterwards, and its general lack of a deformational fabric is related to its strength as more ductile rocks deformed around it. Recent work on landslide exposures in the High Peaks indicates that although original igneous textures are well preserved in the interior of the Marcy anorthosite massif, some areas show thin, zones of highly deformed rock along lithologic contacts (Chiarenzelli et al. 2015). This implies the transfer of strain from tectonism into the interior of the massif in favorable locations. The reason for AMCG plutonism, including the Marcy anorthosite massif, which underlies the Adirondack High Peaks region, is less clear. Models suggesting the inevitable detachment of a down going slab of oceanic crust or delamination of the crust and mantle during collision have been proposed (McLelland et al. 2010a). Regardless of the reason, the production of large quantities of anorthosite involves the fractional crystallization of large

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amounts of plagioclase from a basaltic magma derived from the mantle. Basalt is readily produced in copious quantities beneath mid-ocean ridges where the Earth’s asthenosphere bulges upward and undergoes a small amount of partial melting due to decompression. A similar origin has been proposed for the Adirondack Suite where the ponding of basalt at the base of the crust would lead to massive melting of the lower crust and the production of felsic or granitic igneous rocks that rose upwards along with the anorthosite. This provides an explanation of coeval nature of the suite but still accounts for their different source regions (felsic or granitic rocks – lower crust; anorthosite – upper mantle).

1150-1100 MILLION YEARS AGO – QUIESCENCE (?) Relatively little is known for sure about the period between 1150-1100 million years ago in the Adirondack Region. It may have been a period of time during which tectonic processes slowed or halted temporarily. Some igneous rocks are thought to have been intruded during this time (Chiarenzelli and McLelland 1991), but they are generally similar in their chemical composition to the earlier AMCG suite. Further, reinvestigation has revealed that they may be older than originally thought. On the other hand, rocks in the Grenville Province in Quebec fall within this time window and late plutonism associated with the AMCG suite or a younger suite of similar origin cannot be ruled out. There is relatively little evidence for voluminous magmatism, deformation, or rapid uplift in this time interval. This may, however, be an artifact of our incomplete knowledge, and we may have to look further afield to understanding what was going on in the context of a tectonic scale. By 1100 million years ago, voluminous volcanic and plutonic rocks associated with the enormous Mid-Continent Rift centered in the Lake Superior Region marked the initiation of extension of the crust (Stein et al. 2014). The Mid-Continent Rift eventually failed, but not before its largest arm propagated all the way south to Oklahoma and produced thick accumulations of rhyolite and basalt now exposed in the Upper Peninsula of Michigan and adjoining areas of Wisconsin, Minnesota, and Ontario. Given the relative proximity, on a plate tectonic-scale, to the Adirondack Region (one arm of the rift extends underneath Michigan to the western end of Lake Erie and possibly all the way to Alabama), farfield plutonic rocks or other effects associated with mid-continent extension are a distinct possibility. Further research will likely explore this possibility.

1100-1050 MILLION YEARS AGO – PLUTONISM, HIGH-GRADE METAMORPHISM, AND EXTENSION, AND THE OTTAWAN OROGENY Granites, pyroxene syenites, fayalite-bearing granites, and leucogranitic rocks ranging in age from 1100-1050 Ma are well known in the Adirondack Highlands (McLelland et al. 1988) but are lacking in the Lowlands (Peck et al. 2013). This has led many workers to surmise that the rocks of the Lowlands were located higher in the crust and escaped deformation and metamorphism (and accompanying plutonism) and/or were located at a distance from their current location in a lateral sense. One consequence of continental collision is the shortening VOLUME 21

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and thickening of the crust and rock units may be moved many hundreds, if not thousands, of kilometers. Some workers have proposed that parts of the Grenville Province are part of an extensive orogenic “lid” (Rivers 2008). Orogenic lids are regions high in the crust during deformation, like the current Tibetan Plateau, which is not currently deforming due to its previous tectonic uplift despite the intensive tectonism beneath it deep in the crust. Essentially, these areas were “along for the ride” but not deformed during it. A logical question, then, is how did the Lowlands come to be juxtaposed against the higher grade Adirondack Highlands and avoid intrusion by these late plutonic rocks? The answer lies along the boundary between the Highlands and Lowlands, known as the CarthageColton Mylonite (or Shear) Zone (CCSZ) for the two North Country towns that mark its end points where it is covered by younger Paleozoic rocks. Workers have confirmed the intrusion of late, syntectonic, 1040 Ma leucogranites along this structure (Selleck et al. 2005). Their syntectonic nature confirms that they were intruded during active deformation. Thus we know, regardless of the earlier, high-temperature history of the CCSZ, the two terranes were brought together at the same crustal level by ca. 1040 Ma. Extensional normal faults like these are common in the late stages of an orogeny and mark the beginning of its long collapse and eventual return to normal crustal thickness via erosion and associated isostatic uplift. In contrast, rocks of the Adirondack Highlands were profoundly affected by the Ottawan Orogeny (ca. 1090-1020 Ma), particularly in the eastern portion of the Adirondacks (McLelland et al. 2001). Our understanding of the deformation that occurred at this time is hampered by high-grade metamorphism; with some workers suggesting the entire crustal architecture of the Adirondacks was produced by this event and others suggesting its effects were more localized. In any event, a profound metamorphic pulse was felt throughout much of the Highlands during this time. It resulted in melting in some rock types, the growth of new metamorphic zircon, and partial to complete resetting of zircon ages in other lithologies. Perhaps the most profound event that occurred between ca. 1100-1040 Ma was the intrusion of a vast amount of leucogranite and related rocks named the Lyon Mountain Granite for the host rock of the large iron deposits on Lyon Mountain in northern New York (Lupulescu et al. 2015). Rocks of this type are found in a large arcing belt extending from the eastern to western Adirondacks Highlands along the northern margin of the topographic dome. They also can be found in various locations within the central portion of the Highlands around the High Peaks. Associated with these rocks are numerous iron deposits that were discovered near the western shore of Lake Champlain and elsewhere and exploited from the late 1700’s until relatively recently. These iron deposits are relatively unique in that they are mostly composed of magnetite and apatite (Lupulescu et al. 2015). In addition, the apatite can contain as much as 20 wt% rare earth elements, which are in high demand because of their essential role in many modern electrical devices. Since the Lyon Mountain Granite appears to have escaped much, or all, of the deformation associated with Ottawan Orogeny (ca. 1090-1020 Ma), it may well be post-orogenic and 30

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would thus place a lower limit on the deformation associated with the Ottawan Orogeny. Postorogenic igneous suites throughout the world consist of voluminous, alkali-rich, leucogranitic rocks. They have a highly evolved chemistry and concentrate some of the less common elements including the lighter rare earth elements, indicating derivation from melting of the deep crust. In many areas, they intrude faults and shear zones and are often associated with hydrothermal fluids and retrograde metamorphism, which is highly dependent on the addition of water to rocks that were essentially dried out by prograde metamorphism. The Lyon Mountain Granite has all the hallmarks of a post-orogenic suite, including the lack of a deformational fabric and high-grade metamorphic mineral assemblages, cross-cutting relationships with other older rock types, intrusion along extensional faults and shear zones, association with ores and hydrothermally altered rocks, and appropriate geochemical and petrologic trends. In addition, study of zircon from Lyon Mountain Granite bodies indicates that some samples have a large amount of inherited cores from the crustal rocks they were derived from (McLelland et al. 2001). Zircon is a very robust mineral and often survives melting. Many of the cores are about ca. 1150 million years in age and indicate partial melting of the voluminous AMCG suite in the Highlands deep in the crust. Thus, the Lyon Mountain Granite appears to an essential part of the orogenic cycle in the Adirondacks and formed as the typical product of the extensional phase of the region. Its vast volume may have supplied part of the heat required to drive the metamorphic growth of zircon and develop hydrothermal convection cells along faults.

1050-1000 MILLION YEARS AGOâ&#x20AC;&#x201D;CONTINUED COLLAPSE, THE TERMINAL RIGOLET PHASE As noted above, much of the Lyon Mountain Granite intruded at ca. 1040 Ma. In some locations, it is itself intruded by iron ore and granitic pegmatites. Geochronology on zircon and monazite from various iron ores, late granite pegmatites, and other associated rocks yield ages that fall between 1040 Ma and 990 Ma (Lupulescu et al. 2011). These ages suggest that the intrusion of post-orogenic rocks continued on for several tens of millions of years, as might readily be expected. Some sections of the Grenville Province, mostly to the north and east of the Adirondacks, show renewed deformation and metamorphism at ca. 1000 Ma, and this event has been named the Rigolet pulse of the Grenville Orogenic Cycle (Rivers 2008). Aside from a few late intrusions, the growth of some metamorphic zircons and monazite, there is little direct evidence that the Rigolet was an important part of the history of the Adirondack Region. However, new data can always necessitate rethinking its role in the region.

1000-540 MILLION YEARS AGOâ&#x20AC;&#x201D;UPLIFT, EROSION, AND RIFTING Our understanding of the long history between the end phases of the Grenville Orogenic Cycle and the deposition of Paleozoic sedimentary rocks in the Adirondack Region is limited by an absence of evidence. The assembly of Rodinia was followed by its eventual VOLUME 21

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rifting (Figure 2), and plate tectonic reconstructions show that by 750 million years ago, the margins of Laurentia were beginning to appear. Rifting is associated with uplift of continental crust along fault systems that eventually form the new plate boundaries. This uplift and associated faulting likely enhanced the erosion and exposure of the once deeply buried Proterozoic basement. Some of the major north-northeast trending faults within the Adirondacks may have been activated during this rifting. The new ocean basin that opened to the east of the Adirondacks has been named the Iapetus, and the later Cambrian and Ordovician sedimentary rocks were deposited along the shore of that ocean.

Figure 5: A series of schematic cross-sections showing the evolution of Adirondack and surrounding regions from NW to SE. Arrows show direction of asthenospheric flow, tectonic movement or stress (green – extension; red – convergence; blue – strike-slip motion). Plutonic suites shown as inverted teardrops (red - calc-alkaline arc plutonism; green – AMCG suite; pink – late post-tectonic granites and leucogranites. Sedimentary rocks of the Grenville Supergroup are shown in orange.

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540-440 MILLION YEARS AGO: THE PALEOZOIC ROCKS The Paleozoic, or ‘Secondary’ sedimentary rocks of the Adirondack region, are part of a sequence of layered strata that extend over much of North America. These strata were deposited on the continental interior during periods of global sea level high stand and tectonic events that caused submergence of the continental crust. Mapping of the geology of the Adirondack region in the 19th century focused on these sedimentary rocks for economic reasons. The limestone and dolostone strata provided material for agricultural lime-making, mortar and cement manufacture, and flux for iron smelting. The sandstones provided quartz sand for glass-making and solid but workable rock for building; the shales were worked for road fill and, when weathered, provided clay for brick and ceramic manufacture. While the older ‘Primary’ rocks, now called the Proterozoic basement, held economic value in metal ores and building stone, it is not surprising that Ebenezer Emmons (1838, 1841), in his reports on the second geological district of New York, paid special attention to the Paleozoic sedimentary rocks and their distribution in and around the Adirondack Massif. In this section, we briefly describe these sedimentary rocks, their distribution, and the geological history they record. While the Adirondacks are most well-known to geologists for its ‘crystallines’ (e.g., coarse grained gneiss, marble, and anorthosite), the Paleozoic strata provide insights into the landscape and evolution of the region over later periods of earth history.

THE LATER RECORD The sedimentary rocks of interest in the Adirondack Region are confined to the early part of the Paleozoic era, the Cambrian (~540-490 million years ago), and Ordovician (~490445 million years ago) (Figure 6). The Paleozoic strata were laid down on top of eroded Adirondack basement, made up of the igneous and metamorphic rocks described earlier in this paper. The metamorphic conditions experienced by these basement rocks require burial to depths of 25 km or more, during the interval 1300 to 1000 million years ago. Yet, by early Cambrian time, the current surface of Adirondack basement was exposed, as the basement directly underlies sediment deposited at the earth’s surface. The mass of material eroded away from the ancient Adirondacks was immense, but so was the interval of time available— nearly 500 million years.

THE GREAT FLOODING OF THE CAMBRIAN 540 million years ago, as the ocean basins of the planet continued to open rapidly, global sea level rose and flooded the low lying edges of the continents. The edge of Laurentia was slowly subsiding as well, after the rifting apart of Rodinia. Along the hot, dry coast of Laurentia, in the Adirondack Region, beaches, shallow water tidal systems, coastal sand dunes, and braided streams deposited quartz-rich sand. These thin sand units were laid down on top of the deeply eroded basement rocks and, when buried and lithified, formed the oldest widespread Cambrian unit in the region – the Potsdam Sandstone, now known

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as the Potsdam Group (Lowe et al. 2015). We use the term â&#x20AC;&#x2DC;unconformityâ&#x20AC;&#x2122; to describe the contact between the Potsdam and the much older metamorphic and igneous basement. The Potsdam is thickest (nearly 300 m), in the northeastern Adirondack margin in Clinton County and is much thinner or absent from the stack of Paleozoic strata along the western Adirondack margin in the Black River Valley. There, the basal sandstone was never deposited or was eroded away before younger rocks were deposited on top of the basement. The Potsdam sandstones are mostly made of quartz sand grains along with other hard, resistant minerals such as zircon. Zircon can be dated using U-Pb techniques, and the ages we get from Potsdam zircons show that while much of the sand was derived from rocks of the same age as the local Adirondack basement crystallines, some sand must have come from much older basement to the north and west in central Canada. The Potsdam is known for its red-pink hues, colors that are caused by tiny iron and titanium oxide crystals that formed during burial and uplift episodes. The Potsdam is widely used as a building stone, particularly along the northern Adirondack margin (e.g., in Malone and Potsdam). Figure 6: Schematic illustration of events and sedimentary rock units in the Adirondack Region. The Little Falls and Galway Formations are part of the Beekmantown Group. The sequence at Wells, NY includes the Potsdam, Beekmantown, Black River, Trenton, and Utica (W on diagram); only Black River and Trenton Group strata are present in the Black River Valley (BRV), where Proterozoic basement directly underlies Paleozoic strata.

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LATE CAMBRIAN SEA LEVEL RISES AND FALLS, AND LIMEY SEDIMENTS ARE LAID DOWN The Potsdam Group in the southern and eastern Adirondack Regions is followed by lime (calcium carbonate) sediment mixed with quartz sand (Galway Formation). The Galway is overlain by the Little Falls Formation, a dolomite rock (dolomite is an Mg-Ca carbonate mineral) that was laid down in very shallow tidal flats where algal heads (stromatolites) were common. The famous Little Falls or Herkimer â&#x20AC;&#x2DC;diamondsâ&#x20AC;&#x2122; are very clear, well-formed quartz crystals that grew in open spaces within the rock during burial, when warm fluids circulated in the strata. The Galway, Little Falls, and overlying limestone and dolostones of uppermost Cambrian and lower Ordovician age (the Beekmantown Group) were deposited in shallow seas that episodically withdrew during short intervals of global sea level fall, only to re-flood the shallow continental area during modest sea level rise. This rising and falling and rising pattern makes for a complicated distribution of these shallow water strata, with some areas receiving little or no sediment at certain times, and areas subject to erosion of older sediment.

THE CRUST BUCKLES UP, AND SEDIMENTATION STOPS FOR A WHILE During the latter part of early Ordovician time, and into early late Ordovician time, much of eastern North America stood above sea level as tectonic plate configuration began to change. The beginning of collisional tectonics of the Taconic Orogeny caused the continental crust to bulge up above sea level across most of the Adirondack region. During this period, the Cambrian and early Ordovician strata previously laid down were subject to erosion and weathering, and in some areas, completely stripped away. This period of uplift, and later deposition of late Ordovician sediments, produced the so-called Knox unconformity, representing a contact between older and younger marine sediments, separated by a period of erosion. This feature is much less grand than the unconformity separating the basal Potsdam sandstones from the underlying Proterozoic basement but is an important signature of the changing tectonic landscape of eastern North America.

COLLISION AND SUBSIDENCE IN THE LATE ORDOVICIAN The Taconic Orogeny involved the successive collision of island arcs (think Japan) with the eastern margin of Laurentia. Those collisions telescoped rocks and sediment from the continental edge up onto the continent, resulting in loading of the continental crust with new material. This loading caused the interior of the continent, in the vicinity of the Adirondacks, to subside, allowing the seas to advance into the continental interior once again. The subsidence took place by bending of the crust, and locally, faults developed that accommodated the subsidence. Along the easternmost Adirondack margin, this subsidence allowed the seas to invade, and limestones of the Chazy Group were deposited. The Chazy is famous for its reefs, which are buildups of limestone sediment in areas where corals, algae, and other hard skeletal organisms were able to thrive. The reefs of the Chazy Group are best

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seen on the islands in northern Lake Champlain. More widespread limestone sediments were deposited following Chazy Group deposition as the Black River Group, which is made up of light to dark grey limestones found along the western, southern, and eastern Adirondack margins. These limestones are commonly used as building stone and for other purposes such as road metal and concrete aggregate. The Black River Group is succeeded by the Trenton Group, which most commonly is made up of limestone beds interbedded with thin layers of dark shale. The Trenton was overall deposited in somewhat deeper water than the Chazy and Black River Groups as a consequence of the continued subsidence of the continental crust during the ongoing Taconic Orogeny. Trenton limestones are often very fossiliferous, with abundant brachiopods, bryozoans, and trilobites among the common fauna.

THE WATER DEEPENS AND THE SEDIMENTS DARKEN The continued collisional tectonics of the Taconic Orogeny caused the Adirondack region to subside even more into the late Ordovician. In addition, mud derived from the uplifted land areas in the collisional zone to the east began to make its way across the region. The deeper, muddier water was less hospitable to organisms that make lime sediment, and the deposition of Trenton Group limestone was followed by accumulation of black mud rich in organic carbon that formed the shale of the Utica Formation. The Utica was first deposited in the eastern part of this shale basin, while limestone sediments were still accumulating in the western, shallower region. However, the foundering of the interior platform soon allowed dark mud to overtake the deposition of limestone, and the Utica spread across the basin. As the Ordovician drew to a close, coarser silt and sand made its way into the basin, and subsidence slowed, allowing shallower water sediments to build up, eventually filling the basin to near sea level. These sedimentary units that overlie the deep water Utica Formation include the Frankfort and Schenectady Formations, which are found to the south of the Adirondacks in the Mohawk Valley, and the Lorraine and Pulaski Formations, found in the Black River Valley and Tug Hill regions.

LATER ON, BURIAL AND UPLIFT Our record of Paleozoic sedimentary strata in the Adirondack region ends with the latest Ordovician. However, the sedimentary rocks now exposed at the surface show plenty of evidence of having been buried to greater depths during the later Paleozoic. Based on the â&#x20AC;&#x2DC;thermal maturityâ&#x20AC;&#x2122; of organic compounds (oil and gas precursors in shale), the temperatures recorded by precipitation of minerals from hot water (e.g., Herkimer Diamonds), and the minerals present in volcanic ash beds (e.g., in the Black River and Trenton Groups), we estimate that the Paleozoic rocks currently at the surface were buried to depths of three or more kilometers across the Adirondack region. This means that additional younger

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sedimentary rocks of Silurian and Devonian age were present above the Adirondacks and were eroded away. To the south of the region, rocks of these ages occur as part of the thick sedimentary sequence of the northern Appalachian Basin. Uplift of the region likely began in early Mesozoic time, based on the ages recorded by fission tracks in minerals such as apatite (Roden-Tice et al. 2000).

A PRECIOUS PALEOZOIC RECORD IN THE WELLS OUTLIER One might be tempted to ask at this point “If the Adirondacks have Proterozoic rocks at the surface, how do we know that this early Paleozoic history you just described is really true?” A very important record of the Paleozoic of the Adirondacks is found in the vicinity of Wells, New York. At Wells, normal faults have dropped down a block of Cambrian and Ordovician strata and preserved that record within the south-central Adirondacks (see Valentino et al. this volume). The Wells Outlier, a down-faulted area or graben, includes the Potsdam Group, Galway Formation, and Little Falls Formation, of Cambrian age, as well as the Black River and Trenton Groups and Utica Formation, of upper Ordovician age. Smaller outliers are found along similar normal fault valleys in the Adirondack region, but the Wells example is our most well-known. Exposures of the Paleozoic units are found within Wells Village and also in a rock quarry (permission required to visit).

SUMMARY The Adirondack Mountains of New York form a small but significant portion of the Grenville Province, the bulk of which is exposed mostly in eastern Canada. Relatively recent vertical uplift has moved Adirondack rocks that were part of the roots of billion year old global system of mountain belts and exposed them at the surface. The rocks in the Adirondacks range in age from 1350-1000 million years old and record many of the events associated with the Grenville Orogenic Cycle, whose duration and complexity is similar to that of the Appalachian Orogeny, although they formed nearly a billion years earlier. Active tectonism and magmatism occurred, with some hiatuses, between ca. 1250 to 1000 million years ago in response to a series of tectonic events that affected the Grenville Province. Recent work has emphasized the importance of the Shawinigan Orogeny and its temporal links to intrusion of the Marcy anorthosite massif and associated granitic plutonic rocks. Metasedimentary rocks of the Grenville Supergroup can be used to decipher the region’s pre-tectonic history. The region’s location in the approximate center of a highly eroded and ancient mountain belt makes it ideal to study processes that occurred deep in the crust, and evaluate the tempo and architecture of mountain building in the distant past. The younger Paleozoic sedimentary rocks are a minor part of the Adirondack geological story but provide important records of the Cambrian and Ordovician history of the region and of later plate tectonic processes. The existence of fault-bounded, Paleozoic outliers, within the central part of the Adirondack dome, has much to tell us about the timing and nature of uplift of the region.

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ACKNOWLEDGEMENTS

J. Chiarenzelli would like to thank the family and friends of Archie F. MacAllaster and Barbara Torrey MacAllaster for their sponsorship of his Chair in North Country Studies and the family and friends of James Henry Chapin for his Chair in Mineralogy and Geology. B. Selleck gratefully acknowledges support from the Macolm and Sylvia Boyce Fund and the Thomas A. Bartlett Chair Fund, both of Colgate University, for research on the Adirondack region. Both authors would like to thank all the contributors to this special issue on the Geology of the Adirondack Region and the staff and contributors to the Adirondack Research Consortium. Without your support this issue could not have happened. Both authors would like to thank Caleb Northrop and the Adirondack Research Consortium Board for their support of this volume. This article was reviewed by William Peck and we thank him for his insightful comments. JRC would like to acknowledge the editorial assistance of Ms. Lisa Grohn and Ms. Larissa De Santana Do Nascimento. MORE ABOUT PALEOZOIC ROCKS IN AND AROUND THE ADIRONDACKS

Apart from the examples mentioned here, and to get much more detailed information about rocks and where they are best found, seek out the website of the New York State Geological Association (http://www.nysga-online. net/). Guidebooks from the association’s annual meetings are available for free download after three years, and more recent guidebooks can be purchased in hard copy using the website. Recent meetings of interest include 2002 (Lake George), 2004 (Potsdam), 2008 (Lake George, again), 2012 (Clinton), 2014 (Alexandria Bay), and 2015 (Plattsburgh). All but the last two years are currently available for free download.

L I T E R AT U R E C I T E D

Carr, S.D., R.M Easton, R.A. Jamieson, and N.G. Culshaw. 2000. “Geologic transect across the Grenville Orogen of Ontario and New York,” Canadian Journal of Earth Sciences, 37: 193-216. Chiarenzelli, J. and J. McLelland. 1991. “Age and regional relationships of granitic rocks in the Adirondack Highlands,” Journal of Geology, 99: 571-590. Chiarenzelli, J., M. Lupulescu, S. Regan, D. Valentino, and D. Reed. 2015. “The Bennies Brook Slide: A Window into the core of the Marcy Anorthosite: Trip A-2,” Annual New York State Geological Association Field Conference Guidebook, 87: 133-166. Chiarenzelli, J., M. Lupulescu, E. Thern, and B. Cousens. 2011. “Tectonic implications of the discovery of a Shawinigan ophiolite (Pyrites Complex) in the Adirondack Lowlands,” Geosphere, 7: 333-356.

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Corrigan, D. 1995. Mesoproterozoic evolution of the south-central Grenville orogen: structural, metamorphic, and geochronological constraints from the Maurice transect. Ph.D. thesis, Ottawa: Carleton University, 308 pp. deLorraine, W.F. 2001. “Metamorphism, polydeformation, and extensive remobilization of the Balmat zinc orebodies, northwest Adirondacks, New York,” Guidebook Series Society of Economic Geologists [U.S.], 35: 25-54. Dickin, A.P. and R.H. McNutt. 2007 “The Central Metasedimentary Belt (Grenville Province) as a failed back-arc rift zone; Nd isotope evidence,” Earth and Planetary Science Letters, 259: 97-106. Emmons, E. 1838. “Report of the second geological district of the state of New York,” New York Geologic Survey, Annual Report, 2: 185-252. Emmons, E. 1841. “Fifth annual report of the survey of the second geological district of New York,” New York Geologic Survey, Annual Report, 5: 113-136. Gates, A., D. Valentino, J. Chiarenzelli, G. Solar, and M. Hamilton. 2004. “Exhumed Himalayan-type syntaxis in the Grenville Orogen, northeastern Laurentia,” Journal of Geodynamics, 37: 337-359. Hanmer, S., D. Corrigan, S. Pehrsson, and L. Nadeau. 2000. “SW Grenville Province, Canada; the case against post-1.4 Ga accretionary tectonics,” Tectonophysics, 319: 33-51. Heumann, M.J., M.E. Bickford, B.M. Hill, J.M. McLelland, B.W. Selleck, and M.J. Jercinovic. 2006. “Timing of anatexis in metapelites from the Adirondack lowlands and southern highlands; a manifestation of the Shawinigan Orogeny and subsequent anorthositemangerite-charnockite-granite magmatism,” Geological Society of America Bulletin, 118: 1283-1298. Hoffman, P.F. 1991. “Did the breakout of Laurentia turn Gondwanaland inside out?” Science, 252: 1409-1412. Isachsen, Y.W. 1981. “Contemporary doming of the Adirondack mountains: further evidence from releveling,” Tectonophysics, 71: 95-96. Lowe, D., R. Brink, and Ch. Mehrtens. 2015. “Sedimentology and Stratigraphy of the Cambrian-Ordovician Potsdam Group (Altona, Ausable and Keeseville Formations), Northeastern New York,” Annual New York State Geological Association Field Conference Guidebook, 87: 120-161. Lupulescu, M.V., J.R. Chiarenzelli, D. Bailey, and S. Regan. 2015. “The magnetite-fluorapatite ores from the Eastern Adirondacks, New York: Cheever Mine: Trip B-1,” Annual New York State Geological Association Field Conference Guidebook, 87: 133-166.

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Lupulescu, M.V., J.R. Chiarenzelli, A.T. Pullen, and J.D. Price. 2011. “Using pegmatite geochronology to constrain temporal events in the Adirondack Mountains,” Geosphere, 7: 23-39. McLelland, J.M. and J.R. Chiarenzelli. 1990. “Geochronological studies in the Adirondack Mountains and the implications of a middle Proterozoic tonalitic suite,” Special Paper Geological Association of Canada, 38: 175-194. McLelland, J., J Chiarenzelli, P. Whitney, and Y. Isachsen. 1988. “U-Pb zircon geochronology of the Adirondack Mountains and implications for their geologic evolution,” Geology, 16: 920-924. McLelland, J., J.S. Daly, and J.M. McLelland. 1996. “The Grenville orogenic cycle (ca. 13501000 Ma): an Adirondack perspective,” Tectonophysics, 265: 1-28. McLelland, J., M. Hamilton, B. Selleck, D. Walker, and S. Orrell. 2001. “Zircon U-Pb geochronology of the Ottawan Orogeny, Adirondack Highlands, New York; regional and tectonic implications,” Precambrian Research, 109: 39-72. McLelland, J.M., B.W. Selleck, and M.E. Bickford. 2010a. “Review of the Proterozoic evolution of the Grenville Province, its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians,” in R.P. Tollo, M.J. Bartholomew, J.P. Hibbard, and P.M. Karabinos, (Eds.). From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region, Geological Society of America Memoir, 206: 1-29. McLelland, J.M., B.W. Selleck, M. Hamilton, and M.E. Bickford. 2010b. “Late- to posttectonic setting of some major Proterozoic Anorthosite-Charnockite-Mangerite-Granite (AMCG) Suites,” Canadian Mineralogist, 48: 1025-1046. Moore, J.M. and P.H. Thompson. 1980. “The Flinton Group: a late Precambrian metasedimentary succession in the Grenville Province of eastern Ontario,” Canadian Journal of Earth Sciences, 17: 1685-1707. Moretton, K. and A.P Dickin. 2013. “Nd isotope mapping of the Dysart gneiss complex: Evidence for a rifted block within the Central Metasedimentary Belt of the Grenville Province,” Precambrian Research, 228: 223-232. Peck, W.H., B.W. Selleck, M.S. Wong, et al. 2013. “Orogenic to postorogenic (1.20-1.15 Ga) magmatism in the Adirondack Lowlands and Frontenac Terrane, southern Grenville Province, USA and Canada,” Geosphere, 9: 1637-1663. Rainbird, R.H., V.J. McNicoll, R.J. Thériault, L.M. Heaman, J.G. Abbott, D.G.F. Long, and D.J. 1997. “Pan-Continental River System Draining Grenville Orogen Recorded by U-Pb and Sm-Nd Geochronology of Neoproterozoic Quartzarenites and Mudrocks, Northwestern Canada,” The Journal of Geology, 105: 1-17.

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Rivers, T. 2008. “Assembly and Preservation of lower, mid, and upper orogenic crust in the Grenville Province-Implications for the evolution of large hot long-duration orogens,” Precambrian Research, 167: 237-259. Rivers, T. and D. Corrigan. 2000. “Convergent margin on southeastern Laurentia during the Mesoproterozoic: Tectonic implications,” Canadian Journal of Earth Sciences, 37: 359-383. Roden-Tice, M., S.J. Tice, and I.S. Schofiled. 2000. “Evidence for differential unroofing in the Adirondack Mountains, New York State, determined by apatite fission-track thermochronology,” Journal of Geology, 108: 155-169. Selleck, B., J.M. McLelland, and M.E. Bickford. 2005. “Granite emplacement during tectonic exhumation: The Adirondack example,” Geology, 33: 781-784. Smith, T.E. and M.J. Harris. 1996. “The Queensborough mafic-ultramafic complex; a fragment of a Meso-Proterozoic ophiolite? Grenville Province, Canada,” Tectonophysics, 265: 53-82. Stein, C.A., S. Stein, M. Merino, G.R. Keller, L.M. Flesch, and D.M. Jurdy. 2014. “Was the Midcontinent Rift part of a successful seafloor-spreading episode?” Geophysical Research Letters, 41: 1465–1470. Valentino, D., J. Chiarenzelli, D. Piaschyk, L. Williams, and R. Peterson. 2008. “The Southern Adirondack Sinistral Transpressive Shear System,” Friends of the Grenville Field Trip 2008, Indian Lake, New York, 56 pp.

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“ T he conical shape of the mountains formed of this rock [anorthosite], has led to the popular opinion that the region is volcanic; and accounts are often related, of lights being seen, explosions heard, and sulphur smelt. But in no part of the Adirondack group is there a trace of a crater, or any sign distinctly volcanic, either ancient of modern, except in the trap dykes which are so common throughout the whole territory.” Ebenezer Emmons GEOLOGY OF NEW YORK: SURVEY OF THE SECOND GEOLOGICAL DISTRICT

1842

CHAPEL POND SLAB

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EPISODES IN GEOLOGICAL INVESTIGATIONS OF THE ADIRONDACKS WILLIAM H. PECK

Department of Geology, Colgate University, Hamilton, NY 13346, wpeck@colgate.edu

KEYWORDS:

Bedrock Geology, Anorthosite, Geology of New York, Historical Geology, Early Maps, New York State Geological Survey

INTRODUCTION The crystalline rocks of the Adirondacks are now recognized to preserve a record of magmatism and metamorphism formed during Proterozoic tectonic episodes, but to early workers their origin was not obvious. After reconnaissance in the early 19th century, it became clear that rocks of the Adirondacks sit below the Potsdam Sandstone and other Paleozoic strata and contain a variety of igneous and metamorphic rocks that record a complicated, multi-stage history. Subsequent work focused on untangling these relationships, but basic questions about how particular Adirondack rocks formed persisted well into the 20th century, which saw the incorporation of Adirondack Geology into plate-tectonic theory. This contribution broadly summarizes the history of geological investigations of the Adirondacks, with a focus on the 19th and early 20th century, and provides a somewhat brief summary of more recent developments.

EARLY INVESTIGATIONS The first geological map of the United States does not include the Adirondack Mountains (Figure 1). This map covering the eastern states was published in 1809 by William Maclure [1763-1840], a wealthy Scottish émigré. Maclure, the “father of American Geology,” was well-traveled, conversant with the geology of Europe, and surveyed the geology of the eastern seaboard during 1808 and 1809 (Doskey 1988).

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This early geological map represents one of the first attempts anywhere to synthesize the geology over a large area by use of color to represent rock units. In 1817, Maclure’s updated Observations on the Geology of the United States of America and map (Figure 2) were published, incorporating new geological data and an expanded discussion including “the boundaries of the great primitive formation, north of the Mohawk” (Maclure 1817), referring to the thenunnamed Adirondack Mountains. Maclure’s maps used the nomenclature of the influential Prussian geologist Abraham Gottlob Werner [1749-1817], subdividing American geology into Primitive (oldest), Transition, Secondary, and Alluvial (youngest) rocks. In this system, Primitive rocks such as those in the Adirondacks represent the oldest kind of rocks and are devoid of fossils, with fossil-bearing sedimentary rocks being younger and sitting at stratigraphically higher levels. Maclure (1817) colored Primitive rocks “sienna brown” on his map and recognized the classification as including most igneous and metamorphic rocks: “Granite, Gneiss, Mica Slate, Clay Slate, Primitive Limestone, Primitive Trap, Serpentine, Porphyry, Sienite [syenite], Topaz-rock, Quartz-rock, Primitive Flinty-slate, Primitive Gypsum, and White-stone.”

Figure 1 (top): Section of Maclure’s 1809 geological map of the United States of America (Maclure 1809). Orange= Primitive rocks, Red= Transition rocks, Blue= Secondary rocks, Yellow= Alluvial rocks. Inset shows the outline of New York and Precambrian exposure of the Adirondacks. From davidrumsey.com.

Figure 2 (bottom): Section of Maclure’s 1818 geological map of the United States of America (Maclure 1818). Orange= Primitive rocks, Red= Transition rocks, Blue= Secondary rocks, Green= Rock Salt, Yellow= Alluvial rocks. Inset shows the outline of New York and Precambrian exposure of the Adirondacks. From davidrumsey.com.

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Maclure made pains to specify that his use of Werner’s classification was not genetic (“Without entering into any investigation of the origin” of the rocks), and that the Wernerian classification seemed the most suitable to him, because it was the most comprehensive and seemed to correspond with the order of formations he had observed in the United States. To Maclure, using Werner’s classification did not mean adopting the accompanying theory of Neptunism – that most rocks (including the Primitive) formed in a regressing world ocean. Maclure was, for the most part, an actualist, and, when theorizing on rock origins, he preferred to classify rocks that are formed by observable causes (such as sedimentary rocks and lavas) separately from rocks that were similar to these but whose origin was more uncertain, such as gneiss, slate, and granite (White 1979). More importantly, Maclure recognized that Primitive rocks probably had a variety of ultimate origins and that a lengthy timescale was required to form them (White 1979). The second major American geological map that covers the Adirondacks is the first geological map of New York by Amos Eaton (1830; Figure 3). With Benjamin Silliman, Eaton [1776-1842] was one of the first American-born geoscientists. Originally trained in law, Eaton’s geology was largely self-taught before beginning a career as a lecturer in Natural History at several institutions across New York and New England. During the 1820s, Eaton rose to prominence in scientific society through his work in geology and biology and by his influence as an educator under the patronage of Stephen Van Rensselaer (Spanagel 2014). Eaton and his assistants made the first systematic geological and agricultural surveys of the area around Albany followed by an extensive geological survey of the route of the Erie Canal. In 1824, he was instrumental in founding the Rensselaer School (later Rensselaer Institute), training many of the prominent American scientists and engineers of the next generation. The late 1820s found Eaton embroiled in a dispute of stratigraphic nomenclature and priority with the English-American geologist George William Featherstonhaugh [1780-1866]. When Featherstonhaugh requested state money to produce a geological map of New York, Eaton quickly enlisted Van Rensselaer’s support to fund a map of his own, first, and to block Featherstonhaugh’s becoming the first state geologist (Aldrich 2000). The resulting map is reasonably close to the modern geological maps for the center of the state where Eaton’s fieldwork had been concentrated, but, especially in the Adirondacks, it is very different (Figure 3). Eaton’s notebooks show that he was perplexed by the geology of the Adirondacks and its connection with other mountain ranges, and he hypothesized that the edges of mountains and river valleys could control or be controlled by the boundaries between geological units (Spanagel 2014). This may have caused Eaton to extrapolate the geology, especially his mapped north-south sedimentary units, into a region for which he had little data. On this part of Eaton’s map, Ebenezer Emmons editorialized later: “It is sufficiently evident that all this was imaginary; it is even difficult to conceive how imagination could have carried even a partial observer so far from the truth” (Emmons 1842).

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When discussing specific occurrences of Primitive rocks Eaton’s (1830) descriptions are almost entirely of localities from New England, and his description of Adirondack geology is for the most part a secondary account of the few early observers in this area. He recognized Primitive rocks as including granite, gneiss, talc-bearing slates, and marble but did not distinguish between these on his geological map. Eaton’s map divided geology into eight units based on rock-type, and the Primary became part of the grey ‘I’ unit, rocks containing graphite (plumbago) and parts of the blue unit, which contains marble, calc-silicate rocks, and limestone (Figure 3). Eaton does not develop a geological history for the Primitive, except to hypothesize that they were deposited as a worldwide layer “before any plants or animals had been created,” and provided the material from which subsequent geological units would be later made (Eaton 1830).

Figure 3 (top): Eaton’s Economical Geology of New York (Eaton 1830). Grey= Carboniferous formations (I: Primitive, II: Transition, III: Lower Secondary, IV: Upper Secondary, V: Tertiary), Yellow= Quartzose formations, Blue= Calcareous formations, Red= Variegated sandstone supporting salt springs or basalt, Green= Lias and ferriferous rocks of a subordinate series. Inset shows the outline of New York and Precambrian exposure of the Adirondacks. From library.si.edu/ digital-library. Figure 4 (bottom): Adirondack marble (limestone) cross-cutting syenite (sienitic granite) (Emmons 1842).

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THE STATE GEOLOGICAL SURVEY In 1836, the New York State Natural History Survey was finally approved by the state legislature, and Governor Marcy appointed four principle geologists for four districts of the state. The Adirondacks lie in the second of four geological districts, and the region was assigned to Ebenezer Emmons [1799-1863]. Emmons was one of three district geologists trained by Amos Eaton at the Rensselaer School and brought with him mineralogical expertise and field experience from work in the Berkshire Mountains and Nova Scotia (Aldrich 2000). Emmons was to spend five field seasons in preparation of the report of the Second District and is best known to later generations of geologists for his involvement in the ensuing Taconic Controversy – a contentious dispute about whether or not metamorphosed sediments in the Taconic Mountains were correlative to (or younger than) un-deformed Paleozoic sediments mapped by the survey elsewhere in New York (Schneer 1969). In the Adirondacks, Emmons was first assisted by James Hall (his later adversary in the Taconic Controversy) and thereafter by his son Ebenezer Emmons Jr. Field work in the Second District concentrated on establishing the lower Paleozoic stratigraphy around the Adirondack periphery, characterization of Precambrian bedrock in the Adirondacks, and was especially focused on topographic and cartographic work in areas of the High Peaks that had not yet been fully surveyed (Aldrich 2000). Emmons coined the term “Adirondacks” to describe the mountain range and led the first group to ascend Mt. Marcy, which he named for New York’s eleventh Governor (Emmons 1837). Emmons’s fieldwork in the second district was partially determined by economic interests, such as a focus on agriculture, surveying a proposed railroad route, and detailed study at working iron mines in the region (Aldrich 2000). The report on the Second District (Emmons 1842) contains detailed descriptions of the Primary (or crystalline) rocks of the Adirondacks. Emmons subdivides Primary rocks into Unstratified (granite, hypersthene rock [anorthosite], primitive limestone [marble], serpentine, Rensselaerite [talc pseudomorphs after pyroxene]), Stratified (gneiss, hornblende, sienite [syenite], talc), and subordinate rocks (porphyry, trap, magnetite, specular hematite) that can occur in either, or younger, rocks. For their economic importance, the iron oxide ore deposits receive the most detailed descriptions, but, of Primary rocks, the Unstratified category is clearly the focus of the scientific interest in the report. A particular interest of Emmons’s is the origin of Primitive limestone [marble], about which he concludes “…I propose to establish the igneous origin of this limestone; following out the train of reasoning by which Hutton has proved the igneous origin of granite, and the great mass of unstratified rocks.” A.F. Buddington (1939) later commented that this was “not a strange conclusion, for [marble] forms dike-like bodies in the country rocks and appears to contain inclusions of them” (Figure 4). Emmons interpreted the Primary Unstratified rocks as igneous, and, of the Stratified category, the sienite, gneiss, and hornblende “at least in some circumstances… to be regarded as of igneous origin.” Likewise, the cross-cutting and discordant nature of magnetite and hematite was also taken as evidence for igneous intrusion.

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On cross-sections and on the state map synthesizing data from the four districts, the rocks of the Adirondacks are assigned to the Primary System but are not further differentiated, although some specific names of rock-types are noted on the cross sections themselves. It is interesting that although Emmons described the geographic distribution of a number of igneous and metamorphic rocks in his report, they do not appear on state geological maps until the last decade of that century (e.g., Figure 5). The second half of the 19th century saw little new geological work in the Adirondacks, and, from the perspective of many geologists, the state survey stood as the authoritative account of the region’s geology:

“ To read a report of results reached, as left by Professor Ebenezer Emmons, is easy; but when we visit the wilderness and test its difficulties, and reflect that Emmons wrote a description of the structure of the Adirondacks forty-five years ago, we become deeply impressed by the energy and skill brought into exercise by the older geologists. To a great extent, the difficult work has been accomplished.” Alexander Winchell WALKS AND TALKS IN THE GEOLOGICAL FIELD

1886 During the late 19th century, there was no settled nomenclature for discussing rocks older than the Cambrian. Lacking fossils for correlation and having no way to determine the absolute age of rocks resulted in a situation where geologists had to rely on lithologic similarity to correlate rock units separated by distance. So often, when distinct Precambrian rocks were described, new sub-divisions of geological time were proposed. This issue came to a head as the US Geological Survey and state surveys tried to reconcile their geological investigations with the nomenclature erected by the Geological Survey of Canada in the 1850s (Eagan 1989). Most important to the Adirondacks is the description of the Laurentian Mountains of Quebec by William Logan [1798-1875], a British-trained geologist and first director of the Geological Survey of Canada (Logan 1863). Logan designated the most deformed and presumably oldest unit in southern Canada as the ‘Fundamental Gneiss’, which he interpreted to be the basement to all subsequent rocks; he also designated a regional metasedimentary package of marbles, quartzites, schists, and amphibolites as the “Grenville Series’, named for its type locality at Grenville village on the Ottawa River. These two rock associations were together assigned to the ‘Laurentian System’. Apparently younger Precambrian rocks elsewhere were designated the ‘Huronian System’ in this classification. This terminology was widely discussed in North American and abroad, and elements of it came to be used by the Geological Survey of Great Britain. James Hall, who at this point had engaged on-and-off with the work of the New York survey for almost

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40 years, believed that marbles and other metasedimentary rocks of the Adirondacks were stratigraphically between the Laurentian and the Cambrian Potsdam Sandstone (Hall 1876), and thus not correlative with the Grenville Series. Late in the century, the similarities and links between the Grenville Series and metasedimentary rocks in the Adirondacks gained more traction with the new generation of American geologists in the Adirondacks (e.g., Smyth 1894). These geologists also took up the new term adopted by Canadian geologists anorthosite to describe the plagioclase-rich rocks of the Adirondack High Peaks (which Emmons had termed “hyperthene rock”).

Figure 5 (top): C. H. Hitchcock’s Geological map of New York (Asher and Adams 1870). Pink= Eozoic, including the Laurentian, Red= Trap (or Dolerite?), Other colors= Paleozoic and Mesozoic units, drift or alluvium. Ultimately derived from the 1842 map produced by the state survey, this geological map is typical of those made during the second half of the nineteenth century where rocks of the Adirondacks are not differentiated, while Paleozoic and Mesozoic rocks are broken into more than a dozen geological units. Inset shows the outline of New York and Precambrian exposure of the Adirondacks. From davidrumsey.com. Figure 6 (bottom): Adirondack sheet of the 1901 Geological map of New York (Merrill 1901). Precambrian rocks of the Adirondacks are shown as patterned light brown (Grenville limestone [marble] and gneiss), patterned dark brown (gneiss), gabbro [including anorthosite] (green), and augite syenite (diagonal patterned red). Inset shows the outline of New York and Precambrian exposure of the Adirondacks with the Adirondack Sheet shown as a rectangle.

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THE BEGININGS OF SYSTEMATIC GEOLOGICAL MAPPING The next phase of geological fieldwork in the Adirondacks was inaugurated by James Furman Kemp [1859-1926], Charles Henry Smyth [1866-1937], and Henry Platt Cushing [1860-1921], who began detailed studies in different areas of Adirondacks in the early 1890s. Within a few years, they were joined in geologically mapping the Adirondacks by other workers, mainly other academic geologists. During the several-decade hiatus of geological work in the Adirondacks since Ebenezer Emmons’s survey, much had changed in the landscape of science in the United States, with colleges providing the possibility for more specialized scientific education and the development of research universities and advanced degrees. Kemp, Smyth, and Cushing were all products of this new system: all had advanced degrees, all had studied geology in Europe, and all were professors themselves (at Columbia, Princeton, and Case Western, respectively). As a result, their studies and subsequent work grew more specialized, incorporating detailed outcrop descriptions, mapping, petrography, and chemical analysis of rocks and minerals to an extent not possible before. It is by this time that enough was known about Adirondack Geology that different Precambrian rock units were first portrayed in state geological maps (Figure 6). The first decade of the 20th century saw the first availability of detailed topographic maps of the Adirondacks. These 1:62,500 scale 15-minute quadrangle maps, produced by the US Coast and Geodetic Survey, allowed for detailed systematic geological mapping in the Adirondacks and comparing the details of distribution of rock types and geological structures of separated areas. Mapped quadrangles and accompanying reports were mainly published by the Geological Survey in the Bulletin series of the State Museum, of which the Survey was now a part. The first quadrangle report published was Geology of the Paradox Lake Quadrangle (Ogilvie 1905), which was the dissertation of Ida Ogilvie [1874-1963], a student of Kemp’s at Columbia. Ogilvie was a Bryn Mawr College alumna, and after her Ph.D. she founded the Geology department at Barnard College. Ogilvie was unusual as one of the few female geologists of her era but typical in that much of the work of mapping the Adirondacks was done by academics working during summers as ‘temporary geologists’ for the survey – many as part of their degree programs. Between 1905 and the beginning of World War II, 34 of the ca. 62 quadrangles making up Precambrian exposure of the Adirondacks were mapped, for the most part by Kemp, Smyth, Cushing, their students and colleagues, and William John Miller [1880-1965] of Hamilton College. Quadrangle mapping and the accompanying studies amassed a wealth of detail on the distribution of metasedimentary and igneous rocks, distinguishing different igneous suites and determining their relative ages, and trying to resolve the timing of geological structures. During this period, correlation with the Grenville Series of Canada was well-accepted, and it was observed that many igneous suites post-dated the metasediments and that regional deformation appeared to post-date or be synchronous with igneous intrusion (Buddington 1939). These relationships would prove to be important to the later controversy about the origin of granite.

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It is useful to focus some attention on the career of Arthur Francis Buddington [1890-1980], who was a participant in the flurry of mapping early in the century and an important actor in later petrologic debates about the origin of Adirondack igneous rocks. Buddington finished his Ph.D. with Smyth at Princeton in 1916 and then became involved in Adirondack research when he began a mapping project in the Lake Bonaparte quadrangle. With the US preparing for the possibility of involvement in WWI, Buddington soon became involved in a project to assess Adirondack sulfur resources in Jefferson and St. Lawrence Counties for the New York State Defense Council (Buddington 1917). As for most academic geologists, after the US entered the war, Buddington became part of the war effort: for a time he taught aerial photograph interpretation at Princeton, and later he worked for the US Chemical Warfare Service. After the war, Buddington eventually joined the faculty at Princeton, where his early research focused on the Alaskan Coast Range, spending 16 months in the field there between 1921 and 1925 with the US Geological Survey. When this project ended he returned to Adirondacks, where he would eventually spend 76 months in the field between 1916 and 1960 (Buddington 1970). Buddington wrote or co-authored the Lake Bonaparte (1926), Hammond, Antwerp and Lowville (1934), Santa Cara (1937), Willsboro (1941) Saranac (1953) quadrangle reports, numerous conference abstracts and journal publications on the Adirondacks, and the Geological Society of America Memoir Adirondack Igneous Rocks and their Metamorphism (Buddington 1939). This major publication focused on the northwest Adirondacks, synthesizing his own and others’ mapping with a focus on subdividing and grouping related intrusions. Beginning in 1944, Buddington took on the multi-year project to study iron deposits in the northeast for the U.S. Geological Survey’s Strategic Minerals program, leading to field seasons and ore deposit reports for the Adirondacks, New Jersey, and Pennsylvania (Buddington 1970).

GEOLOGY IN THE ADIRONDACKS AFTER WORLD WAR II Echoing Buddington’s career, geological research in the Adirondacks after the end of WWII had a focus on Adirondack ore deposits: one third of the published research on the Adirondacks in the 1950s (indexed by GeoRef) was on economic geology or the new, related subfield of mineral magnetics. During the period 1900-1959, published scientific research in the Adirondacks was relatively constant, averaging two to three publications per year. Beginning in the 1960s, research in the Adirondacks grew exponentially, reaching a peak of ~70 publications per year in the 1980s. This acceleration in research mirrors the growth of academic science and science funding during the Cold War, and, in the Adirondacks, over half of this research activity was in the area of igneous and metamorphic petrology. Changing approaches to understanding high-grade gneiss terranes and a few full-blown petrologic controversies played out in the Adirondacks during the second half of the 20th century. The first of these was the debate over the origin of granite and granitic rocks, which emerged after WWII, reached its peak in the 1950s, and continued into the 1960s.

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This controversy saw some petrologists dispute the model that granites are formed by crystallization from a silicate melt and instead called on high temperature fluids that transformed already-existing rocks into granitic compositions. This hypothesized process was called granitization and was invoked to explain gradational field relations at granitic pluton contacts and partial melting textures in high-grade gneiss terrains, in effect explaining away the ‘space problem’ associated with the mechanics of pluton intrusion (Davis 2003). Buddington weighed in on the debate as one of five principle speakers at the Geological Society of America’s Origin of Granite conference in 1947. In his address, he laid out field evidence for magmatic intrusion of several Adirondack igneous suites, also describing some replacement of metasedimentary country rocks, which he thought could account for no more than 15% of igneous rocks in the northeastern Adirondacks (Buddington 1948). Granitization as a large-scale process in the Adirondacks was proposed by Albert [19161995] and Celeste Engel [1923-2004], a husband and wife team at the US Geological Survey and later Caltech. Al Engel was first introduced to Adirondack geology by Buddington at Princeton, and after WWII the Engles conducted several petrologic and geochemical research projects rocks and minerals in the northwest Lowlands. Their first granitization study was of element migration and migmatite formation in the Major Paragneiss, an extensive package of metasedimentary rocks in the Lowlands (Engel and Engel 1958). Here metamorphic foliation and layering were taken as reflecting originally sedimentary features; a ‘stratigraphic mindset’ that was common to other Grenville workers of this era (Rivers 2015). The Engels later extended this mode of analysis to the 14 granitic domes now known as the Hyde School Gneiss bodies. Buddington (1929; 1939) had interpreted these domes as phacoliths, being the result of magma intrusion into the axes of actively folding metasedimentary rocks. Hyde School Gneiss geology was reinterpreted by Engel and Engel (1963) and Dietrich (1963), who took the structure of the bodies and their coherent internal layers to indicate a granitized sedimentary sequence. The Engels invited comment from Buddington, who wrote a one-page discussion that appeared in the Geological Society of American Bulletin after their article. In his discussion Buddington (1964) reiterated arguments for intrusion based on field relations, and cited experimental data that showed that the Hyde School Gneiss has the same composition as expected minimum melts in a granitic bulk composition.

THE ‘STRATIGRAPHIC MINDSET’ AND STRUCTURAL MAPPING The origin of the Hyde School Gneiss bodies would continue to be a controversial aspect of Adirondack Lowlands Geology for the next 30 years. This particular dispute notwithstanding, there was broad acceptance of the basic premises that 1) a stratigraphic framework existed in the northwestern Adirondacks and that it could be used to trace

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structural features over large distances and 2) that this stratigraphy was especially useful for understanding the distribution of regional talc and sphalerite deposits (Brown and Engel 1956) to the extent that modified versions of this framework have continued to be used in the Lowlands to the present day. Sedimentary protoliths for some of these units were uncontroversial (e.g., marble and aluminous gneiss), but assigning protoliths to quartzofeldspathic units was generally problematic. The origin of the Hyde School Gneiss was especially unclear, given the concordant contacts and internal structure of the each body and their relatively consistent disposition relative to adjacent units. As a result, the initial interpretation as intrusive bodies (Buddington 1929) and subsequent reinterpretation as granitized sediments (Engel and Engel 1963) was followed by a model where Hyde School Gneiss was interpreted as having a zoned ash-flow tuff protolith that fit conformably into the regional stratigraphy (Foose and Carl 1977; Carl et al. 1990). This model was later disputed based on geochronology, and some of Buddingtonâ&#x20AC;&#x2122;s original lines of argument for plutonic emplacement (McLelland et al. 1991). Disagreement over the pre-deformation geometry and nature of high-grade rocks was not limited to the northwestern Adirondacks. In the 1950s and 1960s, Dirk deWaard and Matt Walton [1915-2004] undertook mapping programs in the central and eastern Adirondack Highlands, where apparently conformable contacts between anorthosite and surrounding metasedimentary rocks led them to interpret the anorthosite as basement to adjacent metasediments, as opposed to being intrusive into the metasedimentary sequence (deWaard and Walton 1967). This interpretation was in fundamental opposition to crosscutting relations documented by early workers, but parallelism of unit contacts caused by structural attenuation of intrusive rocks and country rocks in part led to this interpretation. It was the parallelism of contacts and structural coherence over large distances that led subsequent mappers into the 1970s and 1980s to generalize the intercalated rocks of the Adirondacks in terms of a stratigraphy (although with the anorthosite and related rocks eventually confirmed to be intrusive), a manifestation of the â&#x20AC;&#x2DC;stratigraphic mindsetâ&#x20AC;&#x2122; common to workers in high-grade terrains in the middle 20th century. Commonly in these stratigraphies, quartzofeldspathic gneisses were interpreted as volcanic units in depositional contact with metasedimentary rocks, and along-strike transitions in rock types were interpreted as facies changes (Figure 7; e.g., Wiener et al. 1983), although the possibility that the apparent stratigraphic coherence was imposed by deformation was discussed by some (e.g., Mclelland and Isachsen 1980). The positive result of these trends in research was to encourage workers to try to interpret the structural geology of the Adirondacks over large areas, which allowed them to recognize a multi-stage history of folding and especially regional nappe structures (Figures 8 and 9), an important development in developing tectonic interpretations of the Adirondacks (Rivers 2015).

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Figure 7 (top): Interpreted stratigraphy of Adirondack metasedimentary and metaigneous rocks (Weiner et al. 1983). Figure 8 (bottom): South-southeasterly oriented cross-section of the Adirondacks showing interpreted folding and nappe structure (McLelland and Isachsen 1980).

THE ADIRONDACKS AS A NATURAL LABORATORY FOR PETROLOGY As the field geology of Adirondack igneous and metamorphic rocks became better understood, the Adirondacks became a focus of geologists who were interested in using these constraints to explore fundamental petrologic problems. One example is investigation of the origin of anorthosite, an enigmatic igneous rock composed mostly of plagioclase feldspar that dominates the Adirondack High Peaks. One of the first general papers on anorthosites was

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the influential 1917 The Problem of the Anorthosites by the preeminent experimental petrologist Norman Levi Bowen [1887-1956]. His paper focused on field relations he was shown by Kemp and Cushing in the Adirondacks. It was in the framework of Adirondack field relations that Bowen articulated two questions that have preoccupied petrologists since: the nature of the anorthosite parent magma and the relationship between anorthosite and related granitic rocks (called the anorthosite–mangerite–charnockite–granite suite by later workers). In the Adirondacks, somewhat equivocal field relations and major element geochemistry of these rocks kept these debates alive for decades. A 1966 symposium in honor of A.F. Buddington on the origin of anorthosites saw fourteen papers presented dealing primarily with Adirondack occurrences (Isachsen 1968). For the most part, authors agreed that anorthosite was an igneous cumulate of some kind with a mafic (or intermediate) parent magma, but there was no agreement on the relationship between anorthosite and surrounding granitic plutons. Buddington (1939; 1968) argued that these plutons post-date anorthosite emplacement and were not co-magmatic, while most authors at the anorthosite symposium interpreted gradational field relations and geochemistry as supporting a model where anorthosite and granitic rocks are consanguineous and related by filter pressing or some other mechanism of differentiation. It was not until isotopic investigations in the 1990s of other geological terrains where anorthosite was emplaced into significantly older crust that consanguinity was shown to be inconsistent with the geochemistry of many anorthosites and associated granitic rocks. The Adirondacks also played an important role in the development of metamorphic petrology. The mid-crustal rocks of the Adirondacks were an ideal testing ground for newly-developed metamorphic thermometers and barometers in the 1970s and 1980s, most notably by Eric Essene [1939-2010] and his students at the University of Michigan (Darling and Peck, this issue). The Adirondacks were also a key locality in debates about importance of CO2-rich fluids in the production of high-temperature metamorphic rocks of the granulite facies. This debate (chiefly during the 1980s and 1990s) was called the ‘granulite controversy’ by some to purposely evoke the granite controversy of the 1950s and 1960s and questions as to the role of fluids in metamorphism. The point of contention was a model where the influx of CO2-rich fluids were thought to have stabilized granulite facies minerals and suppressed melting by diluting the chemical activity of water during metamorphism (Newton et al. 1980). Numerous studies of fluid inclusions in minerals, isotope compositions, and estimates of past fluid composition from mineral equilibria in the Adirondacks all argued against pervasive flow of a CO2-rich fluid (Valley et al. 1990). These studies were instrumental in the recognition that metamorphism of granulites often happens in the absence of introduced fluids.

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Figure 9: Adirondack sheet from the 1971 Geological map of New York (Fisher et al.1971; 1995 reprinting). Folded Precambrian rocks of the Adirondacks are subdivided into over two dozen distinct units. Inset shows the outline of New York and Precambrian exposure of the Adirondacks with the Adirondack Sheet shown as a rectangle. From nysm.nysed.gov.

PLATE TECTONICS, ENVIRONMENTAL GEOLOGY, AND OTHER DEVELOPMENTS Several radiogenic isotopic systems were applied to the Adirondacks in the 1960s and 1970s, but the overprinting effects of high-grade metamorphism made interpretations of these data problematic, and basic questions as to the timing of magmatism and metamorphism were still questioned. It was not until U-Pb geochronology studies of igneous suites (e.g., McLelland et al. 1988) and metamorphic minerals (e.g., Mezger et al. 1991) were made across the Adirondacks that the basic chronology was constrained (McLelland, this issue). These studies allowed the first direct correlation of Adirondack geology with the rest of the Canadian Grenville Province, and the development of the first well-constrained plate tectonic models in the 1990s (see Rivers 2015). Beginning in the 1970s, the Adirondacks also saw the rise in interest and focus on environmental geology, especially in the area of surface water chemistry and understanding the effects of acid precipitation (see April, this issue). These research trends have continued into the early 21st century. Currently, published geology research on the Adirondacks (indexed by Georef) ranges from environmental geology to geomorphology to geochronology, and is still dominated by igneous & metamorphic petrology and structural geology studies. New research leads to new questions, and the Adirondacks continues be a place where theories are tested and petrologic tools are developed. The importance of fieldwork to geology, and petrology in particular, is as A.F. Buddington aptly put it 60 years ago:

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“ … I believe it is also true that every advance in geochemistry requires ever greater knowledge and refinement of our knowledge based on field relationships and the two must go forward together, each reacting on the other. A specimen of rock can be treated in the laboratory as an entity in itself. But the significance for geology of the data obtained from it can only be as good as the thoroughness of the knowledge of the nature of the immediate surroundings of the specimen where in place and of its physical and chemical history as read by a field geologist with the appropriate background.” A.F. Buddington ACCEPTANCE OF THE MINERALOGICAL SOCIETY OF AMERICA ROEBLING MEDAL

1957

ACKNOWLEDGEMENTS

I would like to thank the guest editors, Jeff Chiarenzelli and Bruce Selleck, for their invitation to contribute to this volume. My perspective on Adirondack Geology owes a great debt to collaborations over the years with Jeff, Bruce, Jim McLelland, and especially John Valley, who introduced me to the Adirondacks. L I T E R AT U R E C I T E D

Aldrich, M. 2000. New York State Natural History Survey 1836-1842: A Chapter in the History of American Science. Ithaca: Paleontological Research Institution. Asher, J.R. and G.H. Adams. 1870. Asher & Adams’ New Topographical Atlas and Gazetteer of New York, Comprising a Topographical View of the Several Counties of the State. New York: Asher & Adams. Bowen, N.L. 1917. “The problem of the anorthosites,” Journal of Geology, 25: 209-243. Brown, J.S. and A.E.J. Engel. 1956. “Revision of Grenville stratigraphy and structure in the Balmat-Edwards district, northwest Adirondacks, New York,” Geological Society of America Bulletin, 67: 1599-1622. Buddington, A.F. 1917. “Pyrite and pyrrhotite veins in Jefferson and St. Lawrence counties, N.Y.,” New York State Defense Council Bulletin, 1: 40 pp. Buddington, A. F. 1929. “Granite Phacoliths and their contact zones in the northwest Adirondacks,” New York State Museum Bulletin, 281: 51-107. Buddington, A.F. 1939. “Adirondack igneous rocks and their metamorphism.” Geological Society of America Memoirs, 7: 1-343.

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Buddington, A.F. 1957. “Acceptance of the Roebling medal of the Mineralogical Society of America,” American Mineralogist, 42: 259-261. Buddington, A.F. 1963. “Metasomatic origin of large parts of the Adirondack phacoliths: a discussion,” Geological Society of America Bulletin, 74: 353-354. Buddington, A.F. 1969. “Adirondack anorthositic series,” New York State Museum and Science Service Memoir, 18: 215-231. Buddington, A.F. 1970. Unpublished Autobiography, 219 pp. Carl, J.D., W.F. Delorraine, D.G. Mose, and Y-.N. Shieh. 1990 “Geochemical evidence for a revised Precambrian sequence in the northwest Adirondacks, New York,” Geological Society of America Bulletin, 102: 182-192. De Waard, D. and M. Walton. 1967. “Precambrian geology of the Adirondack highlands, a reinterpretation,” Geologische Rundschau, 56: 596-629. Dietrich, R.V. 1963. “Banded gneisses of eight localities,” Norsk Geologisk Tidsskrift, 43: 89-119. Doskey, J.S. 1988. The European Journals of William Maclure. Philadelphia: American Philosophical Society. Eagan, W.E. 1989. “The debate over the Canadian Shield, 1880-1905,” Isis, 80: 232-253. Eaton, A. 1830. Geological text-book: prepared for popular lectures on North American geology; with applications to agriculture and the arts. Albany: Websters and Skinners. Emmons, E. 1837. “First annual report of the second geological district of the state of New York,” Documents of the Assembly of the State of New York, 161: 97-150. Emmons, E. 1842. Geology of New York, Part 2, Comprising the Survey of the Second Geological District. Albany: W. A. White and J. Visscher. Engel, A.E.J. and C.G. Engel. 1963. “Metasomatic origin of large parts of the Adirondack phacoliths,” Geological Society of America Bulletin, 74: 349-352. Engel, A.E.J., C.G. Engel, A.A. Chodos, and E. Godijn. 1958. “Progressive metamorphism and granitization of the Major Paragneiss, northwest Adirondack Mountains, New York part 1: Total rock,” Geological Society of America Bulletin, 69: 1369-1414. Fisher, D.W., Y.W. Isachsen, and L.V. Rickard. 1971. “Geologic Map of New York State,” New York State Museum and Science Service Map & Chart Series, 15.

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Foose, M.P. and J.D. Carl. 1977. “Setting of alaskite bodies in the northwestern Adirondacks, New York,” Geology, 5: 77-80. Hall, J. 1876. “Note upon the geological position of the serpentine limestone of northern New York, and an inquiry regarding the relations of this limestone to the Eozoon limestones of Canada,” American Journal of Science [third series], 12: 298-305. Isachsen, Y.W., Ed. 1969. “Origin of anorthosite and related rocks,” New York State Museum and Science Service Memoir, 18: 466 pp. Logan, W.E. 1863. Geology of Canada; Geological Survey of Canada, Report of progress from its commencement to 1863. Montreal: Dawson Brothers. Maclure, W. 1809. “Observations on the geology of the United States, explanatory of a geological map,” Transactions of the American Philosophical Society, 6: 411-428. Maclure, W. 1817. Observations on the Geology of the United States of America: With Some Remarks on the Effect Produced on the Nature and Fertility of Soils, by the Decomposition of the Different Classes of Rocks; and an Application to the Fertility of Every State in the Union, in Reference to the Accompanying Geological Map. Philadelphia: Abraham Small. McLelland, J., and Y. Isachsen. 1980. “Structural Synthesis of the Southern and Central Adirondacks: A Model for the Adirondacks as a Whole and Plate-Tectonics Interpretations,” Geological Society of America Bulletin, 91(2): 208-292. McLelland, J., J. Chiarenzelli, and A. Perham. 1992. “Age, field, and petrological relationships of the Hyde School Gneiss, Adirondack lowlands, New York: Criteria for an intrusive igneous origin,” Journal of Geology, 100: 69-90. McLelland, J., J. Chiarenzelli, P. Whitney, and Y. Isachsen. 1988. “U-Pb zircon geochronology of the Adirondack Mountains and implications for their geologic evolution,” Geology, 16: 920-924. Merrill, F.J.H. 1901. Geologic map of New York exhibiting the structure of the state so far as known. Albany: New York State Museum. Mezger, K., C.M. Rawnsley, S.R. Bohlen, and G.N. Hanson. 1991. “U-Pb garnet, sphene, monazite, and rutile ages: Implications for the duration of high-grade metamorphism and cooling histories, Adirondack Mts., New York,” Journal of Geology, 99: 415-428. Newton, R.C., J.V. Smith, and B.F. Windley. 1980. “Carbonic metamorphism, granulites and crustal growth,” Nature, 288: 45-50.

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Ogilvie, I.H. 1905. “Geology of the Paradox Lake Quadrangle,” New York State Museum Bulletin, 96: 308 pp. Rivers, T. 2015. “Tectonic setting and evolution of the Grenville orogen,” Geoscience Canada, 42: 77-124. Schneer, C.J. 1969. “Ebenezer Emmons and the foundations of American Geology,” Isis, 60: 439-450. Smyth, C.H. 1894. “Crystalline limestones and associated rocks of the northwestern Adirondack region,” Geological Society of America Bulletin, 6: 263-284. Spanagel, D.I., 2014. DeWitt Clinton and Amos Eaton: Geology and Power in Early New York. Baltimore: Johns Hopkins University Press. Valley, J.W., R.B. Steven, E.J. Essene, and W. Lamb. 1990. “Metamorphism in the Adirondacks: II. The role of fluids,” Journal of Petrology, 31: 555-596. White G.W. 1979. “William Maclure’s concept of primitive rocks (basement complex),” Geological Association of Canada Special Papers, 19: 251-261. Wiener, R.W., J.M. McLelland, Y.W. Isachsen, and L.M. Hall. 1984. “Stratigraphy and structural geology of the Adirondack Mountains, New York: Review and synthesis,” Geological Society of America Special Papers, 194: 1-56. Winchell, A. 1886. Walks and talks in the Geological Field. New York: Chautauqua Press. Young, D.A. 2003. Mind over magma: the story of igneous petrology. Princeton University Press.

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METAMORPHIC CONDITIONS OF ADIRONDACK ROCKS ROBERT S. DARLING 1 AND WILLIAM H. PECK 2

1. Department of Geology, SUNY Cortland, Cortland, NY 13045, 607.753.2923, robert.darling@cortland.edu 2. Department of Geology, Colgate University, Hamilton, NY 13346, 315.228.6798, wpeck@colgate.edu

KEYWORDS:

Adirondacks, Metamorphism, Pressure-Temperature-Path, Fluid Composition, New York

ABSTRACT The Adirondack Highlands were metamorphosed to granulite facies conditions during the Ottawan phase (1090 to 1020 Ma) of the Grenville Orogenic Cycle, whereas the Adirondack Lowlands were metamorphosed to mid to upper amphibolite facies conditions during the Shawinigan phase (1190 to 1140) of the Grenville Orogenic Cycle. Metamorphic temperatures ranged from 750 째C to 850 째C in the Highlands and 650 째C to 750 째C in the Lowlands. Metamorphic pressures were between 6.0 and 8.6 kilobars in the Highlands and 6.5 to 7.5 kilobars in the Lowlands. Following the peak of metamorphism, Adirondack rocks took a counter-clockwise path in pressure-temperature space. The activity of water is generally low in Adirondack metamorphic rocks, and many rocks did not contain a free fluid phase during metamorphism.

INTRODUCTION Ever since Emmons (1842) first reported geological descriptions of the Adirondack region, scores of geologists have travelled to northern New York to study the Mesoproterozoic basement rocks the make up the Adirondack Mountains. Early studies tended to focus on mining and economic resources of the region, but a number of researchers attempted

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to better understand the rocks types and their interrelationships (see Peck, this issue). An emphasis on bedrock mapping occurred in the early part of the 20th century, and a number of 15-minute quadrangle maps were published by the New York State Museum. Later, in his monumental treatise on the Adirondacks, Buddington (1939) summarized descriptions of a wide variety of igneous rock types, compositions, intrusive relationships, and textures but also described and interpreted the structural, textural, mineralogical, and facies changes that occurred in the metamorphic rocks. However, it was not until the late 1950s that metamorphic studies of the Adirondack began to proliferate. Thus, a great deal of effort has been expended on trying to understand the complete history of Adirondack metamorphic rocks and what they can tell us about the Grenville Orogenic Cycle in eastern North America (McLelland, Daly, and McLelland 1996; Tollo, Corriveau, McLelland, and Bartholomew 2004; Rivers 2008). Most attention has been focused on: 1) determining the temperature and pressure conditions of metamorphism, 2) what role fluids play during metamorphism and partial melting, 3) the pressure-temperature path the rocks took while in the crust, and 4) the timing of igneous and metamorphic events in the Adirondacks. This effort has contributed much to our understanding of the Grenville Orogenic Cycle as well as geologic processes in deep parts of the continental crust, but many unanswered questions remain. In this paper, we hope to summarize the current state of knowledge of metamorphism in the Adirondacks but also hope to point out areas where additional work needs to be focused.

ADIRONDACK HIGHLANDS COMPARED TO THE ADIRONDACK LOWLANDS Figure 1A shows the location of Mesoproterozoic rocks of the Adirondack Highlands and Adirondack Lowlands. The two areas are separated by the Carthage-Colton Mylonite Zone, a deep-crustal shear zone with complex kinematic indicators (see Streepey, Johnson, Mezger, and van der Pluijm 2001; Johnson, Goergen, and Fruchey 2004; Baird and MacDonald 2004; Selleck, McLelland, and Bickford 2005, for latest review). The Highlands differ from the Lowlands in two important respects. First, the Highlands were metamorphosed to higher temperature and pressure conditions than the Lowlands (see section on metamorphic facies). Secondly, ages from the collisional Ottawan phase of the Grenville Orogenic Cycle (1090-1020 Ma) dominate the Highlands, whereas ages from the earlier accretionary Shawinigan phase of the Grenville Orogenic Cycle (1160-1140 Ma) characterize the Lowlands (Mezger, Rawnsley, Bohlen, and Hanson 1991; Mezger, Essene, van der Pluijm, and Halliday 1993; Wasteneys, McLelland, and Lumbers 1999; Heumann, Bickford, Hill, McLelland, Selleck, and Jercinovic 2006).

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Figure 1: A) Map showing exposed Mesoproterozoic rocks of northern New York State. Adirondack Highlands and Lowlands are separated by the Carthage-Colton Myonite Zone; B) Metamorphic facies map of exposed Mesoproterozoic rocks in northern New York State. Anorthosite bodies shown in gray shade. Facies boundary is marked by the orthopyroxene (opx)-in isograd as mapped by Hoffman (1982). Note the proximity between the opx-in isograd and the Carthage-Colton Mylonite Zone. Short dashed line represents the maximum stability of muscovite (ms) and quartz (qtz) as mapped by deWaard (1969). Long dashed line is the garnet (gar) + clinopyroxene (cpx) + quartz (qtz)-in isograd as mapped by deWaard (1969).

METAMORPHIC ROCKS OF THE ADIRONDACKS Most of the rocks exposed in the Adirondacks are metamorphic. A small percentage of non-metamorphic rocks occur locally, including: small-scale Mesozoic or late Proterozoic mafic igneous intrusions, undeformed granitic pegmatite dikes of late Ottawan-age, hydrothermal quartz, calcite, and/or fluorite mineralization, tectonic breccias, and faultbounded, Early Paleozoic sedimentary rocks. Many of the metamorphic rocks clearly originated as igneous or sedimentary rocks, but all of them show, to various degrees, a metamorphic fabric and/or growth of new metamorphic minerals. In many cases, bulk rock composition can be used to infer an igneous or sedimentary protolith, but the metaigneous rocks are more likely to preserve primary textures, especially in coarse-grained mafic lithologies. Primary sedimentary structures or textures are all but destroyed in Adirondack meta-sedimentary rocks, with the only exceptions being inferred stromatolite fossils in marbles (Isachsen and Landing 1983) and rare relict cross-beds in quartzites (Engel and Engel 1953) in the Adirondack Lowlands. However, some meta-sedimentary rocks display compositional layering that may reflect original differences in sedimentary rock type (Engel and Engel 1953; Chiarenzelli, Kratzmann, Selleck, and deLorraine 2015). The meta-igneous rocks typically originated as: granites, anorthosites, gabbros, syenites,

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charnockites, tonalites, and mangerites. Meta-sedimentary rocks typically include: marbles, calc-silicate and metapelitic gneisses, and quartzites. Different amphibolites have been interpreted as both meta-igneous as well as meta-sedimentary (Buddington 1939; Engel and Engel 1953). Schists are more abundant in the Lowlands than the Highlands, but in the Adirondack Highlands, biotite is the phyllosilicate phase, as all primary muscovite (Âą quartz) has been converted to K-feldspar + sillimanite, melt, or more rarely, K-feldspar + corundum (Bohlen, Valley and Essene 1985).

ADIRONDACK METAMORPHIC FACIES Metamorphic facies in the Adirondacks have been assigned based on specific metamorphic index minerals or mineral assemblages. In the Adirondack Highlands, for example, it is the presence of metamorphic orthopyroxene in mafic rocks that assign these rocks to the granulite-facies (Figure 1B). Throughout the Adirondack Highlands, metamorphic orthopyroxene has been described in meta-gabbros and anorthosites (Whitney and McLelland 1973; McLelland and Whitney 1977; Whitney 1978), amphibolites (Luther 1976), granitoids (McLelland, Hunt and Hansen 1988a), and even metapelites (Darling, Florence, Lester, and Whitney 2004). The first appearance of orthopyroxene (the opx-in isograd) in Adirondack rocks is proximal to the Carthage-Colton Mylonite Zone (see Figures 1A, B). Hence, the Adirondack Lowlands were metamorphosed to mid to upper amphibolitefacies, whereas the Adirondack Highlands were metamorphosed to granulite-facies (Figure 1B). The opx-in isograd shown in Figure 1A is from Hoffman (1982). Its location is proximal to opx-in isograds mapped earlier by Engel and Engel (1958) and Buddington (1963). Also shown is the maximum stability of muscovite + quartz in the Adirondack Lowlands. Southeast of this isograd, including all of the Adirondack Highlands, sillimanite + microcline are stable in metapelitic rocks. This is sometimes known as the second sillimanite isograd because a substantial modal volume of sillimanite is created by the breakdown of muscovite and quartz. Lastly, running through the central Adirondack Highlands is deWaardâ&#x20AC;&#x2122;s (1965, 1969) garnet + clinopyroxene + quartz-in isograd. This isograd marks the first appearance of garnet in metabasic rocks (e.g., amphibolites, metagabbros) of the central and eastern Adirondack Highlands and accounts for the presence of the famous megacrystic garnet amphibolites at Gore Mountain and elsewhere (McLelland and Selleck 2011). To the west of the isograd, metabasic rocks are characterized by orthopyroxene + plagioclase rather than clinopyroxene + garnet + quartz. DeWaard felt this was such an important isograd that he proposed a subdivision of granulite facies based partially on these mineral assemblages (1965), and inferred that the garnet-free rocks formed under lower pressure conditions. Thus far, no evidence has been found that any part of the Adirondacks experienced eclogite-facies metamorphism, ultra-high temperature (UHT), or ultra-high pressure (UHP) metamorphism.

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TEMPERATURE AND PRESSURE OF METAMORPHISM The temperature and pressure conditions of Adirondack metamorphism have played a significant role in the development of plate tectonic models for the Grenville Orogeny. This is because the temperature and pressure of metamorphism can give useful information on the geothermal gradient as well as the depth of burial, which can be used to infer crustal thickness at the time of metamorphism. Our understanding of metamorphic temperature and pressure in the Adirondacks began to advance in the late 1950s and through the 1960s after important experimental studies were performed on common rock-forming minerals. Thus, Engel and Engel (1958, 1962) and Buddington and Lindsley (1964), began providing the first-ever, quantitative estimates of metamorphic temperature for Adirondack rocks. Their estimates ranged from temperatures of 500 °C to 650 °C. A little later, deWaard (1967, 1969) increased those temperature estimates from 650 °C to 800 °C and for the first time provided quantitative metamorphic pressure estimates of 6 to 8.5 kilobars. More progress was made with additional discoveries of low variance mineral assemblages and the further refinement of geothermometers and geobarometers in the 1970’s. Thus, temperature and pressure estimates made by Bohlen and Essene (1977, 1979), Boone (1978), Bohlen, Essene, and Hoffman (1980), and Bohlen, Essene, and Boettcher (1980) corroborated the estimates of deWaard (1967, 1969). In their summative work, Bohlen and his collaborators used feldspar, carbonate, and Fe-Ti oxide solvus geothermometers to document metamorphic temperatures of 650 °C to 700 °C in the Adirondack Lowlands and 750 °C to 800 °C in the Adirondack Highlands (Bohlen et al. 1985). They also document, using a wide variety of geobarometers and pressure-sensitive mineral assemblages, metamorphic pressures of 6.5 to 7.0 kilobars, in the Adirondack Lowlands, to 7.5 to 8.0 kilobars, in the Adirondack Highlands. Slightly higher pressures (up to 8.6 kilobars) were determined by Newton and Perkins (1982) and Newton (1983). Bohlen et al. (1985) also described a concentric ring-like pattern to metamorphic temperature estimates, with the highest temperatures recorded in the Adirondack high peaks region. This pattern, shown in Figure 2A, is widely known among the metamorphic geology community as “Bohlen’s bull’s-eye.” The significance of Bohlen’s bull’s-eye is unclear. First, the southeast and southwest regions of the Adirondack Highlands have little or no data, and secondly, it is unclear whether much later domical uplift or heat from magmas (Bohlen et al. 1985) or some other processes resulted in higher apparent metamorphic temperatures in the northeast part of the Adirondack Highlands.

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Figure 2: Map showing exposed Mesoproterozoic rocks of northern New York State with: A) metamorphic isotherms (°C) from Bohlen et al. (1985); B) locations of post-1985 metamorphic studies: a) Edwards and Essene (1988), b) Florence et al. (1995), c) Spear and Markussen (1997), d) Alcock and Muller (1999) and Alcock et al. (1999), e) Liogys and Jenkins (2000), f) Darling et al. (2004), g) Peck and Valley (2004), h) Storm and Spear (2005), i) Storm and Spear (2009), and j) Darling (2013). Kitchen and Valley’s (1995) thermometry data for the Highlands are not included, because they used temperatures from Bohlen et al. (1985) to calibrate their calcite-graphite thermometer. However, Kitchen and Valley’s (1995) isotherms are shown in the Lowlands. See text for further discussion.

Since the monumental work of Bohlen et al. (1985), studies of Adirondack metamorphic rocks have either corroborated, or in most cases increased, the metamorphic temperature estimates. Studies by Florence, Darling, and Orrell (1995) and Darling (2013) describe metamorphic temperatures of ≥ 780 °C on the westernmost edge of the Adirondack Highlands. Spear and Markussen (1997), Darling et al. (2004), and Storm and Spear (2009) document similar metamorphic temperatures of 830-870 °C on opposite sides of the Adirondack Highlands (Figure 2B). Pattison (2003a) and Pattison, Chacko, Farquhar, and McFarlane (2003b) argue that temperatures of 800-850 °C characterize all of the Adirondack Highlands. The studies of Peck and Valley (2004) and Storm and Spear (2005) show metamorphic temperatures of 696-772 °C and ≥ 790 °C, respectively, in the southernmost Adirondacks. The study of Kitchen and Valley (1995) shows marbles of the Adirondack Highlands experienced metamorphic temperatures from 670-780 °C. Lastly, Alcock and Muller (1999) and Alcock, Myer, and Muller (1999) report temperatures of 850-970 °C using Al abundance in hornblende and ternary feldspar compositions, but the high temperatures reported were contested by McLelland, Valley, and Essene (2001). There is little dispute with the temperatures on the lower end (~850°C) of their reported range and is shown as such in Figure 2B. All of these later studies demonstrate equivalent, or in many cases, higher metamorphic temperatures than those inferred by Bohlen et al. (1985), but, perhaps more importantly, are inconsistent with metamorphic isotherms mapped by many

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workers (see Bohlen et al. 1985). Consequently, it is difficult to assess whether the earlier mapped isotherms are meaningful. The post-1985 studies have the advantage of generally having newer and perhaps more refined geothermometers, but those geothermometers are restricted to specific mineral assemblages in a few locations, whereas the study of Bohlen et al. (1985) largely used only feldspar and oxide solvus geothermometers that are applicable in a variety of rock types over a wide area. Moreover, the inferred pressure-temperature conditions have been, until recently, assumed to reflect one episode of metamorphism, and this may not be the case in the Adirondack Highlands (see section on Geochronology).

MORE DETAILS ON THE METAMORPHIC CONDITIONS OF THE ADIRONDACK LOWLANDS Compared to the Adirondack Highlands, metamorphism in the Adirondack Lowlands has received less study, especially in the past few decades. Bohlen et al. (1985) and Edwards and Essene (1988) presented the state of knowledge in the mid-1980s for a variety of metamorphic thermometers and phase equilibria that constrain metamorphic pressures. Pressure estimates from these studies range from 5.4-8.0 kbar and are mainly determined from barometers in pelitic rocks. Most determinations tightly constrain pressures in the Lowland to 6.5-7.5 kbar. Metamorphic temperatures from these studies range from 600-780 °C, with most temperatures being in the range 650-750 °C. As in the Highlands, Lowlands thermometry were used to draw regional isotherms, and these are mostly controlled by the results of feldspar thermometry. Lowlands isotherms from these studies separate a low-temperature region in the central Lowlands from high temperatures closer to the periphery and from especially high temperatures in its northernmost part (Figure 2A). This temperature structure has not been confirmed by subsequent studies. Kitchen and Valley (1995) used the carbon isotope fractionation between calcite and graphite in a marbles to map the detailed temperature structure in the Lowlands. This approach yielded similar temperatures to earlier studies with most temperatures in the range 630 °C to 690 °C. A subsequent experimental recalibration of the calcite-graphite thermometer (Deines and Eggler 2009) applied to these data slightly lowers peak temperature estimates to ca. 590-650 °C. Isotherms drawn around these data parallel the structural grain of the Lowlands and mapped isograds and are different than those from earlier studies (Figure 2B); showing a symmetric low-temperature trough in the central Lowlands and higher temperature to the southeast (towards the CCMZ) and the northwest (towards the Black Lake Shear Zone). Supporting this, equivalent temperatures along strike crossing earlier isotherms were reported by Liogys and Jenkins (2000), who used the calibrated equilibrium between amphibole + clinopyroxene + quartz + plagioclase to calculate metamorphic temperatures ranging from 619-758 °C (Figure 2B). Northeast-southwest isotherms are also confirmed by the 39Ar-40Ar age structure of the Adirondack Lowlands, which suggests tilting of the terrane to the northwest (Dahl, Pomfrey, and Foland 2004). In detail, the higher metamorphic temperatures in the northwest Lowlands are not consistent with the Dahl et al. (2004) southeast-younging cooling ages, which may indicate that the higher peak

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temperatures in the northwest recorded by calcite-graphite isotopic equilibria (and other thermometers; Russell, Will, Peck, Perkins, and Dunn 2009) may not be synchronous with peak metamorphism in the rest of the Lowlands.

THE HIMALAYAN TECTONIC MODEL The Himalayan tectonic model applied to the Ottawan phase of the Grenville Orogenic Cycle is based principally on metamorphic pressure measurements and the associated inferred crustal thickness estimate. Thus, the 8.6 kilobar maximum pressure (Newton 1983) means that present-day Adirondack rocks were buried to a depth of about 30 km (assuming 3.5 km of crustal rock per kilobar of pressure) during the peak of the Ottawan phase. If this 30 km depth is added to the 35 ± 2 kilometer (km) thick present-day continental crust under the Adirondacks (Klemperer 1987), the total thickness during the Ottawan phase was 65 ± 2 km. The only location on Earth today where the thickness of continental crust is about 70 km is under the Himalaya Mountains of southeast Asia (Nábělek 2009). Thus, the mountains formed during the Ottawan phase of the Grenville Orogeny were once as tall as the present-day Himalayas (Boone 1978; McLelland, Geraghty, and Boone 1978), and a continent-continent collision tectonic model is invoked for the Ottawan phase of the Grenville Orogenic Cycle (McLelland et al. 1996; Tollo et al. 2004; Rivers 2008).

PRESSURE-TEMPERATURE TIME PATH OF ADIRONDACK ROCKS Equally important to understanding the tectonic history of Adirondack rocks is the relationship between pressure and temperature that the rocks experienced while in the crust (i.e., the PT-path). Mineralogical evidence formed during heating and burial (i.e., the prograde path) is commonly destroyed with progressive metamorphism (Bohlen 1987) and Adirondack rocks are no exception. Thus far, no evidence of the prograde metamorphic path has been reported. The retrograde path, however, has supporting evidence although it is incomplete. Bohlen et al. (1985) and Bohlen (1987) argue that a counter-clockwise retrograde path (i.e., early isobaric cooling followed by later isothermal decompression in a plot of pressure vs. temperature) is supported by: 1) chemical zoning of Fe in garnet rims from ilmenite + sillimanite + quartz + garnet + rutile assemblages and garnet + plagioclase + orthopyroxene + quartz assemblages, and 2) the presence of coarse primary sillimanite as the dominant Al2SiO5 phase. Similarly, Spear and Markussen (1997) show that metamorphic ortho- and clinopyroxene in meta-anorthosite from the northeastern Adirondack Highlands grew along a path where pressure decreased by 6 bars per 1 ºC from about 830 °C to 700 °C. Further cooling led to garnet growth between 575 °C and 675 °C at pressures of ~ 6 kilobars (Spear and Markussen 1997). A counter-clockwise PT path is further supported by Lamb, Brown, and Valley (1991) who studied H2O + CO2 fluid inclusions in Adirondack rocks and found steep isochores (lines of equal fluid density in PT space) in the latter part of the retrograde path. This study was further supported by Darling and Bassett (2002), who increased the minimum temperatures and pressures along the isochores. Both studies

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demonstrate that H2O + CO2 fluid inclusions, trapped during the retrograde path of Adirondack rocks, were very dense fluids, which is the opposite of what is expected and found in rocks taking a clockwise PT path to the surface (i.e., isothermal decompression followed by isobaric cooling). Well-documented clockwise retrograde metamorphic paths like those from the Himalayas (see Beaumont, Jamieson, Nguyen and Lee 2001) also contain low density H2O + CO2 fluid inclusions (Craw 1990; Craw, Koons, Zeitler, and Kidd 2005; Derry, Evans, Darling, and France-Lanord 2009). The counter-clockwise retrograde metamorphic path preserved in the Adirondacks is unusual for a continent-continent collision. Typically, when continents collide, burial occurs at a faster rate than the rocks can warm resulting in a clockwise PT path (England and Thompson 1984). It appears an opposite process was operating in the Adirondacks, that is, the rocks were hot before they were buried deeply. This excess heat is thought to be left over from the widespread magma intrusion (anorthosite-mangerite-charnockite-granite) before deep burial during the Ottawan phase of the Grenville Orogeny (Bohlen 1987; Spear and Markussen 1997).

GEOCHRONOLOGY Dating the age of metamorphism was an early goal of geochronology in the Adirondacks and was an essential part of determining its geodynamic significance, especially the relationship between intrusion of plutons and metamorphic heating. Early K-Ar dating led to the recognition that the Adirondacks and the Canadian Grenville Province were younger than other regions of the Precambrian Canadian Shield, yielding ages of ca. 1100-800 Ma (Doe 1962; Harper 1968), in most cases reflecting cooling of the rocks. Rubidium-strontium isochron geochronology proved to be difficult to apply in the Adirondacks, especially in meta-igneous rocks where dates could not unequivocally be assigned to igneous crystallization or subsequent metamorphism. Thus, ages of 1110-1030 Ma for intrusions and their country rocks (e.g., Hills and Gast 1964) could be taken as evidence for synmetamorphic intrusion or for isotopic resetting of the igneous rocks during later metamorphism. It was not until broad application of the robust U-Pb isotope system to well-constrained samples that the multiple igneous suites of the Adirondacks could really be distinguished (McLelland and Chiarenzelli 1989) and that the diachronous thermal history of the Highlands and Lowlands was recognized. In the Adirondack Lowlands, U-Pb ages of refractory metamorphic minerals are 1168-1127 Ma, while those of the Highlands are ca. 100 m.y. younger: 1064-1033 Ma (Mezger et al. 1991). Both Highlands and Lowlands rocks cooled at an average rate of approximately 1.5 Â°C/m.y. following their respective thermal peaks (Mezger et al. 1991; Dahl et al. 2004). There is also evidence for earlier 1180-1160 Ma metamorphism and partial melting in the Highlands (Mezger et al. 1991; Heumann et al. 2006). Thus, metamorphism, as expressed in rocks of the Lowlands, was synchronous with voluminous 1155 Ma anorthosite-suite magmatism in the Highlands (McLelland et al. 2001), but the most recent metamorphism in the Highlands is later and overprints some anorthosite-suite rocks. As a result, in the Highlands

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metamorphism of the 1090-1020 Ma Ottawan phase are most clearly reflected by mineral assemblages and compositions of 1155 Ma anorthosite-suite rocks (Bohlen et al. 1985; Spear and Markussen 1997), while older metasedimentary rocks experienced both Ottawan and Shawinigan events (e.g., Florence et al. 1995, Kitchen and Valley 1995; Peck and Valley 2004; Darling et al. 2004; Storm and Spear 2005). In the absence of direct dating of metamorphic minerals in these rocks, it is unclear if metamorphic assemblages that represent the Shawinigan orogeny were reset during Ottawan heating or if they reflect a combination of the two events. An example of this is the ≥790 °C, 7-9 kbar metamorphic determinations of migmatitic pelites of the southern Adirondacks (Storm and Spear 2005), where zircon associated with partial melting of these rocks has Shawinigan ages, but the majority of matrix monazite and monazite inclusions in garnets have Ottawan ages. These data are taken to indicate that the rocks melted during Shawinigan metamorphism but were not able to melt again during anhydrous Ottawan metamorphism (Heumann et al. 2006); phase equilibria and themobarometry of these rocks, however, reflect Ottawan conditions (Storm 2005). More work of this sort is required to unravel the polymetamorphic history of the Highlands. Only in a few localities of the Highlands are field relations amenable to isolating Shawinigan mineral assemblages, most notably foliated xenoliths included in anorthosite-suite rocks that preserve pre-1155 Ma metamorphism and deformation (McLelland, Lochhead, and Vyhnal 1988b; McLelland and Chiarenzelli 1989). Sillimanite + K-feldspar assemblages in pelitic xenoliths (McLelland et al. 1988b) indicate that Shawinigan metamorphism reached granulite or near-granulite conditions, broadly similar to Ottawan metamorphism.

CONTACT METAMORPHISM Early work on the Proterozoic terrains noted the common association of massif anorthosite with high-grade metamorphism, and, lacking geochronological constraints, a causal relationship between magmatic heating and metamorphism was often assumed. This was the case in the Adirondack Highlands, where ca. 8 to 9 kbar (27 to 31 km) metamorphic pressures retrieved from anorthosite-suite pyroxenes were understood to indicate deep anorthosite intrusion during the metamorphic event (e.g., Jaffe, Robinson and Tracy 1975; Ollila, Jaffe and Jaffe 1988). The abundance of wollastonite at anorthosite contacts, as well as more uncommon contact-metamorphic minerals, such as akermanite and monticellite, are best explained by formation at low pressures during contact metamorphism and preservation during later fluid-absent granulite facies metamorphism (Valley, Bohlen, Essene and Lamb 1990). Most importantly, wollastonite + garnet + diopside skarns that formed in the northeastern contact zone of the anorthosite in the Willsboro-Lewis area have restrictively low oxygen isotope ratios. Low oxygen isotope ratios (δ18O as low as -1.3‰ SMOW) in skarn minerals are indicative of interaction with heated meteoric water (Valley and O’Neil 1982; Clechenko and Valley 2003), a feature shared by anorthosites in the southern contact zone of the massif (Morrison and Valley 1988a). Most primary skarn

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minerals were recrystallized during Ottawan deformation, but zoned andradite-grossular skarn garnets formed during anorthosite emplacement are locally preserved in areas of low strain (Clechenko and Valley 2003). The presence of large volumes of surface fluids during intrusion constrains emplacement of the anorthosite to shallow depths (<10 km; Valley and O’Neil 1982). This recognition was an important line of evidence that contact metamorphism could not be the primary heat source for regional granulite-facies metamorphism, and this was confirmed by U-Pb geochronology in the 1980s and 1990s, which solidified the timing of anorthosite intrusion (1155 Ma) and Ottawan metamorphism (1090-1020 Ma). Decoupling these geologic events also allowed for the recognition that the thermal effects of anorthosite-suite magmatism could sometimes be distinguished from overprinting regional metamorphism. In the Highlands, carbon isotope ratios at the cores of graphites are consistent with ca. 860-890 °C contact metamorphic temperatures near the anorthosite massif, while graphite rims grew at regional Ottawan temperatures (Kitchen and Valley 1995). The other major igneous suite in the Adirondacks that shows evidence for contact metamorphism is the Hyde School Gneiss (HSG) of the Lowlands. The origin of the HSG bodies has historically been a source of controversy and has been interpreted at different times as plutons, granitized metasediments, and metamorphosed ash-flow tuffs (Peck, this issue). It is now recognized that this plutonic suite was emplaced at depth during the peak of Shawinigan metamorphism, at ~1172 Ma (Wasteneys et al. 1999) and that aluminous rocks found at the boundaries of the HSG preserve evidence of contact metamorphism. In these rocks, quartz + spinel assemblages yield metamorphic temperatures ≥875 °C (Powers and Bohlen 1985), corundum + spinel + sillimanite + garnet assemblages yield temperatures 780-810 °C (McLelland, Chiarenzelli, and Perham 1992), and garnet-biotite thermometry yields peak temperatures of 830-860 °C (Hudson 1994), all of which are to 200 °C above the regional Shawinigan temperature structure of the Lowlands.

METAMORPHIC FLUIDS Investigations of metamorphic petrology coupled with better understanding of Adirondack geochronology in the 1970s-1990s allowed detailed petrologic and isotopic studies to constrain fluid composition and flow during metamorphism (see Valley et al. 1990). The lack of widespread melting in granitic rocks during granulite facies metamorphism indicates low water activity, and mineral equilibria that buffer a(H2O) yield low and variable water activities in a variety of Adirondacks rock types (≤0.2 in the Highlands and ≤0.5 in the Lowlands). Some assemblages that are very restrictive of fugacities of fluid components can be used to demonstrate that those rocks did not contain a free fluid during metamorphism, while other rocks appear to have been fluid-saturated. Outcrop-scale variability in a(H2O), a(CO2), f(O2), and other constraints on fluid composition demonstrate that metamorphic fluid flow, if present, was not pervasive and that in most cases fluid compositions were buffered by the local rocks. This conclusion is supported by steep isotopic gradients and minimal diffusion across lithologic contacts (Valley et al. 1990; Cartwright and Valley 1991).

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The low a(H2O) in many Adirondack rocks is interpreted to have been mainly caused by a combination of metamorphism of already anhydrous igneous rocks and by desiccation of rocks by partitioning of water into partial melts (Valley et al. 1990).

RESOLVING THE TIMING OF METAMORPHIC CONDITIONS Although geologists have made great progress in better understanding metamorphism throughout the Adirondacks, a number of unanswered or poorly answered questions remain. First, can strong evidence of pre-Ottawan metamorphism (i.e., Shawiniganage) be found in the Adirondack Highlands, or is the evidence completely overprinted by Ottawan-age heating and burial? If so, it is reasonable to believe that evidence of the equally important prograde Ottawan metamorphic path could be preserved as well. Progress in this area will require coupled geochronologic and geothermobarometric studies with careful attention paid to interpreting textures of relevant minerals so that metamorphic temperature, pressure, and timing are robustly constrained. Second, more data are needed to help refine the pressure, temperature, and timing of the retrograde path of Adirondack metamorphic rocks. This requires new geothermobarometry and geochronologic studies on retrograde mineral assemblages. Part of the problem here is that new mineral growth on the retrograde metamorphic path is uncommon in the Adirondacks, but it is not absent. Chlorite mineralization along fractures in mafic minerals from Gore Mountain (Shaub 1949), healed fractures in Gore Mountain garnet (Ferguson and Darling 2013), secondary calcite mineralization in anorthosite rock fractures (Morrison and Valley 1988b), and chlorite + muscovite mineralization in mylonites from the south-central Adirondacks (Gates, Valentino, Chiarenzelli, Solar, and Hamilton 2004; Price et al. 2003; Valentino, Piaschyk, Price, Freyer, Solar, and Chiarenzelli 2005) all represent new mineral growth under lower temperature and pressure conditions, and, if not the result of Paleozoic burial, may yield important information on the post-Ottawan retrograde path. ACKNOWLEDGEMENT

The authors are grateful to Dr. Jeff Chiarenzelli for a careful and constructive review of this manuscript. L I T E R AT U R E C I T E D

Alcock, J. and P. Muller, P. 1999. “Very high temperature, moderate pressure metamorphism in the New Russia gneiss complex, northeastern Adirondack Highlands, metamorphic aureole to the Marcy anorthosite,” Canadian Journal of Earth Sciences, 36(1): 1-13. Alcock, J., K. Myer, and P.D. Muller. 1999. “Three-dimensional model of heat flow in the aureole of the Marcy anorthosite, Adirondack Highlands, New York: Implications for depth of emplacement,” Geological Materials Research, 1(4): 1-27.

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Baird, G.B. and W.D. MacDonald. 2004. “Deformation of the Diana syenite and Carthage-Colton mylonite zone: Implications for timing of Adirondack Lowlands deformation,” Geological Society of America Memoirs, 197: 285-297. Beaumont, C., R.A. Jamieson, M.H. Nguyen, B. Lee. 2001. “Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation,” Nature, 414: 738-742. Bohlen, S.R. and E.J. Essene. 1977. “Feldspar and oxide thermometry of granulites in the Adirondack Highlands,” Contributions to Mineralogy and Petrology, 62(2): 153-169. Bohlen, S.R., and E.J. Essene. 1979. “A critical evaluation of two-pyroxene thermometry in Adirondack granulites,” Lithos, 12(4): 335-345. Bohlen, S.R., E.J. Essene, and K.S. Hoffman. 1980. “Update on feldspar and oxide thermometry in the Adirondack Mountains, New York,” Geological Society of America Bulletin, 91(2): 110-113. Bohlen, S.R., E.J. Essene, and A.L. Boettcher. 1980. “Reinvestigation and application of olivine-quartz-orthopyroxene barometry,” Earth and Planetary Science Letters, 47(1): 1-10. Bohlen, S.R., J.W. Valley, and E.J. Essene. 1985. “Metamorphism in the Adirondacks. I. Petrology, pressure and temperature,” Journal of Petrology, 26(4): 971-992. Bohlen, S.R. 1987. “Pressure–temperature–time paths and a tectonic model for the evolution of granulites,” Journal of Geology, 95: 617-632. Boone, G.M. 1978. “Kyanite in Adirondack Highlands sillimanite-rich gneiss and PT estimates of metamorphism,” Geological Society of America, Abstracts with Programs, 10: 34. Buddington, A.F. 1939. “Adirondack igneous rocks and their metamorphism,” Geological Society of America Memoirs, 7: 1-343. Buddington, A.F. 1963. “Isograds and the role of H2O in metamorphic facies of orthogneisses of the northwest Adirondack area, New York,” Geological Society of America Bulletin, 74(9): 1155-1182. Buddington, A.F. and D.H. Lindsley. 1964. “Iron-titanium oxide minerals and synthetic equivalents,” Journal of Petrology, 5(2): 310-357. Cartwright, I. and J.W. Valley. 1991. “Steep oxygen-isotope gradients at marble— metagranite contacts in the northwest Adirondack Mountains, New York, USA: products of fluid-hosted diffusion,” Earth and Planetary Science Letters, 107(1): 148-163.

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Chiarenzelli, J., D. Kratzmann, B. Selleck, and W. deLorraine. 2015. “Age and provenance of Grenville supergroup rocks, Trans-Adirondack Basin, constrained by detrital zircons,” Geology, 43(2): 183-186. Clechenko, C.C. and J.W. Valley. 2003. “Oscillatory zoning in garnet from the Willsboro Wollastonite Skarn, Adirondack Mts, New York: a record of shallow hydrothermal processes preserved in a granulite facies terrane,” Journal of Metamorphic Geology, 21(8): 771-784. Craw, D. 1990. “Fluid evolution during uplift of the Annapurna Himal, central Nepal,” Lithos, 24: 137-150. Craw, D., P.O. Koons, P.K. Zeitler, W.S.F. Kidd. 2005. “Fluid evolution and thermal structure in the rapidly exhuming gneiss complex of Namche Barwa–Gyala Peri, eastern Himalayan syntaxis,” Journal of Metamorphic Geology, 23: 829-845. Dahl, P.S., M.E. Pomfrey, and K.A. Foland. 2004. “Slow cooling and apparent tilting of the Adirondack Lowlands, Grenville Province, New York, based on 40Ar/39Ar ages,” Geological Society of America Memoirs, 197: 299-323. Darling, R.S. and W.A. Bassett. 2002. “Analysis of natural H2O+CO2+NaCl fluid inclusions in the hydrothermal diamond anvil cell,” American Mineralogist, 87(1): 69-78. Darling, R.S., F.P. Florence, G.W. Lester, and P.R. Whitney. 2004. “Petrogenesis of prismatine-bearing metapelitic gneisses along the Moose River, west-central Adirondacks, New York,” Geological Society of America Memoirs, 197: 325-336. Darling, R.S. 2013. “Zircon‐bearing, crystallized melt inclusions in peritectic garnet from the western Adirondack Mountains, New York State, USA,” Geofluids, 13(4): 453-459. Derry, L.A., M.J. Evans, R. Darling, and C. France-Lanord. 2009. “Hydrothermal heat flow near the Main Central thrust, central Nepal Himalaya,” Earth and Planetary Science Letters, 286(1): 101-109. deWaard, D. 1965. “A proposed subdivision of the granulite facies,” American Journal of Science, 263(5): 455-461. deWaard, D. 1967. “Absolute P-T conditions of the granulite-facies metamorphism in the Adirondacks.” Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. Series B: Palaeontology, Geology, Physics, Chemistry, Anthropology, 70: 400-410. deWaard, D. 1969. “Facies series and P-T conditions of metamorphism in the Adirondack Mountains.” Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. Series B: Palaeontology, Geology, Physics, Chemistry, Anthropology, 72: 124-131.

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Deines, P. and D.H. Eggler. 2009. “Experimental determination of carbon isotope fractionation between CaCO3 and graphite,” Geochimica et Cosmochimica Acta, 73(24): 7256-7274. Doe, B.R. 1962. “Relationships of lead isotopes among granites, pegmatites, and sulfide ores near Balmat, New York,” Journal of Geophysical Research, 67(7): 2895-2906. Emmons E. 1842. “Geology of New York, Part 2,” Survey of the Second Geologic District, 335-427. Engel, A.J. and C.G. Engel. 1953. “Grenville series in the northwest Adirondack Mountains, New York, Part I: General features of the Grenville Series,” Geological Society of America Bulletin, 64(9): 1013-1048. Engel, A.J., and C.G. Engel. 1958. “Progressive metamorphism and granitization of the major paragneiss, northwest Adirondack Mountains, New York,” Geological Society of America Bulletin, 69: 1369-1414. Engel, A.J. and C.G. Engel. 1962. “Hornblendes formed during progressive metamorphism of amphibolites, northwest Adirondack Mountains, New York,” Geological Society of America Bulletin, 73(12): 1499-1514. England, P.C. and A.B. Thompson. 1984. “Pressure—temperature—time paths of regional metamorphism I. Heat transfer during the evolution of regions of thickened continental crust,” Journal of Petrology, 25(4): 894-928. Ferguson, M.M. and R.S. Darling. 2013. “Secondary CO2 inclusions in Gore Mountain garnet, North Creek, NY,” Geological Society of America, Abstracts with Programs, 45: 72-73. Florence, F.P., R.S. Darling, and S.E. Orrell. 1995. “Moderate pressure metamorphism and anatexis due to anorthosite intrusion, western Adirondack Highlands, New York,” Contributions to Mineralogy and Petrology, 121(4): 424-436. Gates, A.E. D.W. Valentino, J.R. Chiarenzelli, G.S. Solar, and M.A. Hamilton. 2004. “Exhumed Himalayan-type syntaxis in the Grenville orogen, northeastern Laurentia,” Journal of Geodynamics, 37(3): 337-359. Harper, C.T. 1968. “On the interpretation of potassium-argon ages from Precambrian shields and Phanerozoic orogens,” Earth and Planetary Science Letters, 3: 128-132. Heumann, M.J., M.E. Bickford, B.M. Hill, J.M. McLelland, B.W. Selleck, and M.J. Jercinovic. 2006. “Timing of anatexis in metapelites from the Adirondack lowlands and southern highlands: A manifestation of the Shawinigan orogeny and subsequent anorthositemangerite-charnockite-granite magmatism,” Geological Society of America Bulletin, 118(11-12): 1283-1298.

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Hills, A. and P.W. Gast. 1964. “Age of pyroxene-hornblende granitic gneiss of the eastern Adirondacks by the rubidium-strontium whole-rock method,” Geological Society of America Bulletin, 75(8): 759-766. Hoffman, K.S. 1982. Investigation of the orthopyroxene isograd, N.W. Adirondacks. M.S. thesis, University of Michigan. Hudson, R.M. 1994. PTXt constraints on ductile deformation zones within the Adirondack Lowlands. Ph.D. thesis, Miami University (Ohio). Isachsen, Y.W. and E. Landing. 1983. “First Proterozoic stromatolites from the Adirondack massif: Stratigraphic, structural, and depositional implications,” Geological Society of America, Abstracts with Programs, 15: 601. Jaffe, H.W., P. Robinson, and R.J. Tracy. 1975. “Orientation of pigeonite exsolution lamellae in metamorphic augite: correlation with composition and calculated optimal phase boundaries,” American Mineralogist, 60: 9-28. Johnson, E.L., E.T. Goergen, and B.L. Fruchey. 2004. “Right lateral oblique slip movements followed by post-Ottawan (1050–1020 Ma) orogenic collapse along the Carthage-Colton shear zone: Data from the Dana Hill metagabbro body, Adirondack Mountains, New York,” Geological Society of America Memoirs, 197: 357-378. Kitchen, N.E. and J.W. Valley. 1995. “Carbon isotope thermometry in marbles of the Adirondack Mountains, New York,” Journal of Metamorphic Geology, 13(5): 577-594. Klemperer, S.L. 1987. “A relation between continental heat flow and the seismic reflectivity of the lower crust,” Journal of Geophysical Research, 61(1): 1-11. Lamb, W.M., P.E. Brown, and J.W. Valley. 1991. “Fluid inclusions in Adirondack granulites: implications for the retrograde PT path,” Contributions to Mineralogy and Petrology, 107(4): 472-483. Liogys, V.A. and D.M. Jenkins. 2000. “Hornblende geothermometry of amphibolite layers of the Popple Hill gneiss, north-west Adirondack Lowlands, New York, USA,” Journal of Metamorphic Geology, 18(5): 513-530. Luther, F.R. 1976. The petrologic evolution of the garnet deposit at Gore Mountain, Warren County, NY. Unpublished Ph. D. thesis, Lehigh University, 224 pp. McLelland, J.M. and P.R. Whitney. 1977. “The origin of garnet in the anorthositecharnockite suite of the Adirondacks,” Contributions to Mineralogy and Petrology, 60(2): 161-181. McLelland, J., E. Geraghty, and G. Boone. 1978. “The structural framework and petrology of the southern Adirondacks: New York State Geological Association,” 50th Annual Meeting, Guidebook, 58-103.

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McLelland, J., W.M. Hunt, and E.C. Hansen. 1988a. “The relationship between metamorphic charnockite and marble near Speculator, Central Adirondack Mountains, New York,” The Journal of Geology, 455-467. McLelland, J., A. Lochhead, and C. Vyhnal. 1988b. “Evidence for multiple metamorphic events in the Adirondack Mountains, NY, The Journal of Geology, 279-298. McLelland, J. and J. Chiarenzelli. 1989. “Age of xenolith-bearing olivine metagabbro, eastern Adirondack Mountains, New York,” The Journal of Geology, 373-376. McLelland, J., J. Chiarenzelli, and A. Perham, A. 1992. “Age, field, and petrological relationships of the Hyde School Gneiss, Adirondack lowlands, New York: criteria for an intrusive igneous origin,” The Journal of Geology, 69-90. McLelland, J., J.S. Daly, and J.M. McLelland. 1996. “The Grenville orogenic cycle (ca. 13501000 Ma): an Adirondack perspective,” Tectonophysics, 265(1): 1-28. McLelland, J.M., J.W. Valley, and E.J. Essene. 2001. “Very high temperature, moderate pressure metamorphism in the New Russia gneiss complex, northeastern Adirondack Highlands, metamorphic aureole to the Marcy anorthosite: Discussion,” Canadian Journal of Earth Sciences, 38(3): 465-470. McLelland, J.M., and B.W. Selleck. 2011. “Megacrystic Gore Mountain–type garnets in the Adirondack Highlands: Age, origin, and tectonic implications,” Geosphere, 7(5): 1194-1208. Mezger, K., C.M. Rawnsley, S.R. Bohlen, and G.N. Hanson. 1991. “U-Pb garnet, sphene, monazite, and rutile ages: Implications for the duration of high-grade metamorphism and cooling histories, Adirondack Mts., New York,” The Journal of Geology, 415-428. Mezger, K., E.J. Essene, B.A. van der Pluijm, and A.N. Halliday. 1993. “U-Pb geochronology of the Grenville Orogen of Ontario and New York: constraints on ancient crustal tectonics,” Contributions to Mineralogy and Petrology, 114(1): 13-26. Morrison, J., and J.W. Valley. 1988a. “Contamination of the Marcy Anorthosite Massif, Adirondack Mountains, NY: petrologic and isotopic evidence,” Contributions to Mineralogy and Petrology, 98(1): 97-108. Morrison, J., and J.W. Valley. 1988b. “Post-granulite facies fluid infiltration in the Adirondack Mountains,” Geology, 16(6): 513-516. Nábělek, J., G. Hetényi, J. Vergne, S. Sapkota, B. Kafle, M. Jiang, H. Su, J. Chen, and B.S. Huang. 2009. “Underplating in the Himalaya-Tibet collision zone revealed by the HiCLIMB experiment,” Science, 325(5946): 1371-1374.

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Newton, R.C. and D. Perkins, III. 1982. “Thermodynamic calibration of geobarometers based on the assemblages garnet-plagioclase-orthopyroxene (clinopyroxene)quartz,” American Mineralogist, 67(3-4): 203-222. Newton, R.C. 1983. “Geobarometry of high-grade metamorphic rocks,” American Journal of Science, 283: 1-28. Ollila, P.W., H.W. Jaffe, and E.B. Jaffe. 1988. “Pyroxene exsolution; an indicator of highpressure igneous crystallization of pyroxene-bearing quartz syenite gneiss from the High Peaks region of the Adirondack Mountains,” American Mineralogist, 73(3-4): 261-273. Pattison, D.R.M. 2003a. “Petrogenetic significance of orthopyroxene‐free garnet+ clinopyroxene+ plagioclase±quartz‐bearing metabasites with respect to the amphibolite and granulite facies,” Journal of Metamorphic Geology, 21(1): 21-34. Pattison, D.R., T. Chacko, J. Farquhar, and C.R. McFarlane. 2003b. “Temperatures of granulite-facies metamorphism: constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange,” Journal of Petrology, 44(5): 867-900. Peck, W.H., and J.W. Valley. 2004. “Quartz–garnet isotope thermometry in the southern Adirondack Highlands (Grenville Province, New York),” Journal of Metamorphic Geology, 22(8): 763-773. Powers, R.E. and S.R. Bohlen. 1985. “The role of synmetamorphic igneous rocks in the metamorphism and partial melting of metasediments, Northwest Adirondacks,” Contributions to Mineralogy and Petrology, 90(4): 401-409. Price, R.E., D.W. Valentino, G.S. Solar, and J.R. Chiarenzelli. 2003. “Greenschist facies metamorphism associated with the Piseco Lake shear zone, central Adirondacks, New York,” Geological Society of America, Abstracts with Programs, 35: 22. Rivers, T. 2008. “Assembly and preservation of lower, mid, and upper orogenic crust in the Grenville Province—Implications for the evolution of large hot long-duration orogens,” Precambrian Research, 167(3), 237-259. Russell, A.K., C.N. Will, W.H. Peck, D. Perkins, and S.R. Dunn. 2009. “Recent calcitegraphite, Ti-in-biotite, garnet-biotite, and two feldspar thermometry of the Adirondacks Lowlands, NY and the southern Frontenac Terrane, Ontario,” Geological Society of America, Abstracts with Programs, 41(7): 634 Shaub, B.M. 1949. “Paragenesis of the garnet and associated minerals of the Barton mine near North Creek, New York,” American Mineralogist, 34: 573-582.

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Selleck, B.W., J.M. McLelland, and M.E. Bickford. 2005. “Granite emplacement during tectonic exhumation: The Adirondack example,” Geology, 33(10): 781-784. Storm, L.C. 2005. “Methods of deciphering complex thermo-chronological histories of migmatitic metapelites: applications within the Adirondack Highlands, New York,” 254 pp. Storm, L.C. and F.S. Spear. 2005. “Pressure, temperature and cooling rates of granulite facies migmatitic pelites from the southern Adirondack Highlands, New York,” Journal of Metamorphic Geology, 23(2): 107-130. Storm, L.C. and F.S. Spear. 2009. “Application of the titanium‐in‐quartz thermometer to pelitic migmatites from the Adirondack Highlands, New York,” Journal of Metamorphic Geology, 27(7): 479-494. Streepey, M.M., E.L. Johnson, K. Mezger, and B.A. van der Pluijm. 2001. “Early History of the Carthage‐Colton Shear Zone, Grenville Province, Northwest Adirondacks, New York (USA),” The Journal of Geology, 109(4): 479-492. Tollo, R.P., L. Corriveau, J. McLelland, and M.J. Bartholomew. 2004. “Proterozoic tectonic evolution of the Grenville orogen in North America: an introduction,” Geological Society of America Memoirs, 197: 1-18. Valentino, D.W., D. Piaschyk, R. Price, P. Freyer, G.S. Solar, and J. Chiarenzelli. 2005. “Post-to Late-Ottawan retrogression associated with east–west extension in the southern Adirondacks, New York,” Geological Society of America Abstracts with Programs, 37: 9. Valley, J.W. and J.R. O’Neil. 1982. “Oxygen isotope evidence for shallow emplacement of Adirondack anorthosite. Valley, J.W., S.R. Bohlen, E.J. Essene, and W. Lamb. 1990. “Metamorphism in the Adirondacks: II. The role of fluids,” Journal of Petrology, 31(3): 555-596. Wasteneys, H., J. McLelland, and S. Lumbers. 1999. “Precise zircon geochronology in the Adirondack Lowlands and implications for revising plate-tectonic models of the Central Metasedimentary Belt and Adirondack Mountains, Grenville Province, Ontario and New York,” Canadian Journal of Earth Sciences, 36(6): 967-984. Whitney, P.R. and J.M. McLelland. 1973. “Origin of coronas in metagabbros of the Adirondack Mts., NY,” Contributions to Mineralogy and Petrology, 39(1): 81-98. Whitney, P.R. 1978. “The significance of garnet ‘isograds’ in granulite facies rocks of the Adirondacks,” Metamorphism in the Canadian Shield. Geological Survey of Canada, Paper 78-10, 357-366.

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RARE EARTH ELEMENT AND YTTRIUM MINERAL OCCURENCES IN THE ADIRONDACK MOUNTAINS MARIAN V. LUPULESCU, 1 JEFFREY R. CHIARENZELLI, 2 AND JARED SINGER 3

1. Research and Collections, New York State Museum, Albany, NY 12230, Marian.Lupulescu@nysed.gov 2. Department of Geosciences, St. Lawrence University, Canton, NY 13617 3. Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180

KEYWORDS:

Rare Earth Elements, Yttrium, Lyon Mountain Granite, Iron Deposits, Eastern Adirondack Highlands

INTRODUCTION The rare earth elements (REE), formally called lanthanides, are a set of fifteen chemical elements, from lanthanum (La) to lutetium (Lu). Yttrium (Y) is added to this group because it has similar properties and occurs in the same mineral deposits. These elements are divided into low-atomic number, lanthanum to europium (La-Eu), or light rare earth elements (LREE), and heavy-atomic number, gadolinium to lutetium (Gd-Lu), or heavy rare earth elements (HREE). Even though they are called “rare,” they are widely distributed in the Earth’s crust and are present in all types of igneous, metamorphic, and sedimentary rocks. Some of the REE have abundances (relative amount of an element in the Earth’s crust) comparable or higher than gold, mercury, tungsten, tin, arsenic, copper, cobalt, and zinc (Handbook of Chemistry and Physics, 2016). In geology research, REE are used to understand earth processes such as crystal fractionation, partial melting, magma mixing, and absolute age dating of minerals. The REE have high-tech industrial applications and are essential for making hybrid cars, computers, smartphones, color TV, lasers, ceramics, and military devices. For this reason, the United States Geological Survey identified the rare earth element dysprosium as one of the most critical elements in the 2010 Critical Materials Strategy

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report. Significant igneous REE deposits are often associated with unusual igneous rocks such as carbonatites and peralkaline silicate rocks; chemical weathering is another geological process that may concentrate REE in economic abundances (for details, see Elements 2012). In this paper, we discuss the mineralogy, chemical composition, and occurrences of the REE minerals and REE-bearing minerals from the Adirondack Mountains. The mineralogical survey of New York State indicates three types of occurrences as potential sources for the rare earth elements (REE) and yttrium (Y) minerals: (1) Low Ti-Fe oxide (magnetite) â&#x20AC;&#x201C; fluorapatite (LTF); (2) Pegmatite; and (3) Metamorphic-hydrothermal veins. The LTF deposits contain REE- or REE-bearing minerals such as REE-rich fluorapatite, monazite-(Ce), allanite-(Ce), stillwellite-(Ce), and zircon. Allanite-(Ce), fergusonite-(Y), polycrase-(U), and monazite-(Ce) occur in pegmatites and bastnaesite-(Ce), cerian epidote, and kainosite-(Y) are components of the hydrothermal or metamorphic-hydrothermal veins. By far, the most important potential source for the REE in the Adirondack Mountains is fluorapatite from the LTF ores. Figure 1: Hand specimen of magnetite (dark)-fluorapatite (light orange colored) ore from Mineville.

RARE EARTH ELEMENT MINERALS OF THE ADIRONDACK REGION Fluorapatite, Ca5(PO4 )3F (Figure 1), is the most important REE-bearing mineral in New York, both economically and scientifically. It occurs in deposits from eastern Adirondacks (Hammondville, Skiff Mountain, Mineville, and Cheever in Essex County; Palmer Hill, Arnold Hill, Rutgers Mine, and Lyon Mountain in Clinton County). It was first mined in 1852 from Mineville by the Moriah Phosphate Company with the intention of producing fertilizers. The mine initially exploited the outcrop (Figure 2), and the amount of apatite from the surface was greater than it was from the underground works (Maynard 1889).

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The phosphate mineral apatite came to the attention of the Professor Ebenezer Emmons, who supervised the American Mineral Company formed in 1853. The company mined mainly apatite for fertilizers and iron as by-product, but because the market did not react very well to their products, the company had to lease their properties and mineral rights to Port Henry Iron Ore Company (Farrell 1996). Initially, fluorapatite was considered only useful for the production of fertilizers, but after 1940, a U. S. Geological Survey report showed that the phosphate was very rich in rare earth elements. Molycorp, a REE producing company, leased the mineral rights and started their recovery from the tailings, but the feasibility studies were unfavorable and the company did not acquire the property. Interest in the REE-bearing apatite was renewed in 1983, and Williams Strategic Metals of Colorado purchased the fluorapatite-rich tailings then re-sold them in 1986 to Rhone-Poulenc, Inc., a French state-owned company (Farrell 1996). Later, Rhodia Inc. of New Jersey became the owner, and today Solvay, a Belgium company, has the surface and mineral ownership. Figure 2: Outcrop of the magnetite-fluorapatite ore. The 4 inch GPS device is for scale.

Mariano and Mariano (2012) suggested â&#x20AC;&#x153;if there is an urgent need for HREEs in North America, the apatite tailings at Mineville, NY, may be the best sourceâ&#x20AC;? (Figure 3). According to them the tailings embrace 5 million m3 containing 8-9 million kilograms (kg) of Y2O3 with a grade of 0.12% Y2O3 and 0.6% REO. Fluorapatite from the eastern Adirondacks iron deposits displays distinctive concentric zoning or dissolution under scanning electron microscopy (SEM) and cathodoluminescense (CL). Backscattered electron images (BSE) highlight four major types of textures: (a) areas of low BSE intensities within brighter apatite grains, or along crystal margins; (b) fractured fluorapatite with tiny secondary monazite(Ce) and thorite crystals; (c) blobs or rods of quartz in fluorapatite; (d) mantled fluorapatite; (e) monazite-(Ce)- allanite(Ce) Âą fluorapatite symplectite. In all of the above mentioned textural situations, the LREE were leached out and recrystallized as REE minerals (monazite, allanite), but yttrium was always retained by fluorapatite. VOLUME 21

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Stillwellite-(Ce), (Ce,La,Ca) BSiO5, was found at Mineville (Mei et al. 1979) and Cheever, Essex County. The sample from Mineville was collected from the â&#x20AC;&#x153;Old Bedâ&#x20AC;? magnetitefluorapatite ore body in the area of a fault on the 2100 ft-level. It occurs as 1-2 mm-wide tabular crystals with waxy luster and pink to reddish color. Our analyses show the following REE concentration in the mineral: 20.44 lanthanum, 30.83 cerium, 1.51 praseodymium, 7.07 neodymium, and 1.73 samarium, all in weight percent (wt%). It is low in yttrium and thorium. The stillwellite-(Ce) from Cheever displays the same mineral association, properties, and composition. Monazite-(Ce), (Ce,La,Nd,Th)PO4, occurs in LTF deposits and pegmatites. Monazite(Ce) from the LTF deposit is low in xenotime (YPO4) component, but large amounts of lanthanum and neodymium substitute for cerium. Monazite-(Ce) from the Batchellerville pegmatite in Saratoga County displays the following composition: 18.1 cerium, 17.01 thorium, 7.89 lanthanum, 7.12 neodymium, and 1.69 yttrium, all in element wt% (Lupulescu et al. 2012). Xenotime-(Y), YPO4, was found only from the Mayfield pegmatite. Allanite-(Ce), (Ca,Ce)2(Al,Fe2+,Fe3+)3(SiO4)(Si2O7)O(OH), is generally not a very spectacular mineral (it is dark colored) and is of no use at this moment for REE extraction. It is, however, common in the pegmatites (Batchellerville, Saratoga County; Roe Spar Bed, Mineville, Hague, Essex County), and in some magnetite-fluorapatite deposits of the Adirondack Mountains. The most remarkable crystals were found by Blake (1858) at Mineville, on the eastern side of the Adirondacks, in small pegmatite dikes cutting the magnetite ore; the crystals were very large: 20-25 cm long, 6-20 cm wide, and 2.5-5 cm thick. Our analyses indicate that the allanite-(Ce) from Mineville contains 10.10 lanthanum, 12.36 cerium, 2.17 neodymium, and 1.68 praseodymium, all in wt%. Fergusonite-(Y), YNbO4, occurs in intergrowth with allanite-(Ce) at the Roe Spar pegmatite as clusters of crystals 1.5-2.5 inches in length displaying fan-shaped radial sections, adamantine luster, and brown color. Uranopolycrase, (Y,Ca,Ce,U,Th)(Ti,Nb,Ta)2O6, occurs in the Day (Overlook), Saratoga County pegmatite (Smith and Kruesi 1947) as small, dark greenish to brown-black, tabular crystals associated with quartz, feldspar, and/or schorl. It displays pinacoids and domes and few prisms and pyramidal faces. Zircon, ZrSiO4, is very common, occurring at almost all the pegmatite locations, mainly in the metamict state due to its uranium and thorium content. It is very common in the granitic rocks of the Adirondack Mountains. REE-bearing epidote, Ca2(Fe3+,Al)3(SiO4)3(OH), was found from the Coal Mine vein, Rossie, St. Lawrence County in association with allanite-(Ce). Here, it occurs as acicular radial aggregates of greenish crystals on calcite (Robinson et al. 2001). Another occurrence of

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this mineral was described from a metamorphic-hydrothermal vein from Long Lake, Hamilton County (Richards and Robinson 2000). Kainosite-(Y), Ca2(Y,Ce)2Si4O12(CO3)H2O, occurs as millimeter-sized crystals associated with fluorite, REE-bearing epidote, and quartz (Richards and Robinson 2000). The HREE are predominant in the REE budget. Bastnaesite-(Ce), Ce(CO3)F, was described as fine-grained tiny crystals associated with REEbearing apatite from Mineville (McKeowan and Klemic 1956) and in association with quartz in a hydrothermal vein cutting the Potsdam sandstone, Trout Brook Valley, Ticonderoga, Essex County (Doll 1983). Figure 3: Tailings at Mineville, Essex County.

SUMMARY Most of the REE minerals from the Adirondack Mountains have only scientific significance or could be seen as specimens of Museums and mineral collectorsâ&#x20AC;&#x2122; interest. This is the case for the minerals occurring in pegmatites and hydrothermal-metamorphic veins; they are rare or in the form of silicates and therefore are not properly processed for the REE extraction. The tailings from the previously mined LTF deposits contain fluorapatite that is rich in REEs, significantly the heavier REEs, to be of economic interest. United States Geological Survey started an aeromagnetic survey of the eastern Adirondacks in the fall-winter of 2015. A press release from the United States Geological Survey from December 4, 2015 indicated a 450 mi2 area in Essex and Clinton counties will be investigated by aerial geophysical techniques to map buried geological structures associated with iron and REE deposits (USGS 2015). This geophysical investigation will bring information of the deep buried geological structures in this part of the Adirondacks.

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ACKNOWLEDGEMENT

The authors gratefully acknowledge a thorough and insightful review by Bruce Selleck. L I T E R AT U R E C I T E D

Blake, Wm. P. 1858. “Lanthanite and allanite in Essex County, N. Y.,” American Journal of Science, 245. Doll, C.G. 1983. “Bastnaesite near Ticonderoga, New York,” The Mineralogical Record, 239-241. Farrell, P. 1996. Through the light hole. Utica, NY: North Country Books. CRC Handbook of Chemistry and Physics. 2016. William M. Haynes (Ed.), Taylor and Francis, 97: 2653. Lupulescu, M.V., J.R. Chiarenzelli, and D.G. Bailey. 2012. “Mineralogy, classification, and tectonic setting of the granitic pegmatites of New York State, USA,” The Canadian Mineralogist, 50: 1713-1728. Mariano, N.A. and A. Mariano, Jr. 2012. “Rare earth mining and exploration in North America,” Elements, 8: 369-376. Maynard, G.W. 1889. “The iron ores of Lake Champlaine,” Journal of British Iron and Steel Institute, i: 114. McKeown, F.A. and H. Klemic. 1956. “Rare – earth – bearing apatite at Mineville, Essex County, New York,” U. S. Geological Survey Bulletin 1046 – B. Mei, L., R.R. Larson, P.J. Loferski, and H. Klemic. 1979. “Analyses and description of a concentrate of stillwellite from Mineville, Essex County, New York,” U.S. Geological Survey Open-File Report, 79-847. Richards, P.M. and G.W. Robinson. 2000. “Mineralogy of the calcite-fluorite veins near Long Lake, New York,” The Mineralogical Record, 31: 413-422. Robinson, G.W., G.R. Dix, S.C. Chamberlain, and C. Hall. 2001. “Famous mineral localities: Rossie, New York,” The Mineralogical Record, 32: 273-293. Smith, E.S.C. and O. Kruesi. 1947. “Polycrase in New York State,” American Mineralogist, 32: 585-587. USGS. 2015. “Low-flying Airplane Mapping Geology and Mineral Resources Over the Eastern Adirondacks.” Press Release available at https://www2.usgs.gov/newsroom/article. asp?ID=4403.

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MINING, GEOLOGY, AND GEOLOGICAL HISTORY OF GARNET AT THE BARTON GARNET MINE, GORE MOUNTAIN, NEW YORK WILLIAM KELLY

New York State Geologist, Emeritus, Division of Research and Collections, New York State Museum, Albany, NY 12230, kellygeol@msn.com

KEYWORDS:

Garnet, Mining, Gore Mountain, Metamorphism, Lyon Mountain Granite

ABSTRACT Garnet megacrysts commonly 30 centimters (cm) ranging up to 1 meter (m) in diameter occur at the summit of Gore Mountain, Adirondacks, NY and were mined there for abrasives for more than a century. The mine, owned by Barton Mines Co., LLC, is roughly 2 km x 150 m and is located in a hornblende-rich garnet amphibolite at the southern boundary of a metamorphosed olivine gabbro body that is in fault contact with charnockite. Barton supplies garnet, a chemically homogeneous pyrope-almandine, to the waterjet cutting, lapping, and abrasive coatings industries. The garnet megacrysts are reliably dated at 1049 ± 5 Ma. The growth of the garnet megacrysts was facilitated by an influx of hydrothermal fluid emanating from the ore body’s southern boundary fault. The fluids were most probably associated with the intrusion of the Lyon Mountain Granite (1049.9 ± 10 Ma) and/or associated pegmatitic rocks late in the tectonic history of the Adirondacks.

INTRODUCTION The Adirondack Mountains in upstate New York are a small outlier of a larger body of rocks of similar age and geologic history that is located to the north in Canada. The Adirondack region can be loosely divided into amphibolite metamorphic facies Lowlands, in the northwest, and the granulite facies Central Highlands, which are VOLUME 21

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separated by a very large, northwest-dipping fault zone. The rocks that comprise the Barton Mine, Gore Mountain and environs are in the Central Highlands. Gabbroic rocks in the Central Highlands commonly contain garnets, often as crystals of unusual size (i.e., megacrysts up to 1 m in diameter). The garnet deposit at Gore Mountain is the most spectacular (Figure 1), but megacrystic garnets, similar to but smaller than Gore Mountain, occur elsewhere such as at Cranberry Lake, Warrensburg, and Speculator. For discussion of these latter and other Adirondack megacrystic garnet occurrences, the reader is referred to McLelland and Selleck (2011). Typically, the Gore Mountain garnets are roughly dodecahedral single crystals encompassed by an enveloping shell, up to 4 cm thick, of hornblende. On roughly flat surfaces, the hornblende appears as a rim on the garnet. Figure 1: Garnet megacrysts in metamorphosed gabbroic anorthosite, Barton Mine, Gore Mountain. Lens cap is 55 mm. Photo by author.

THE MINE The Barton Mines Corporation open pit mine is located at an elevation of about 800 m on the north side of Gore Mountain. For 105 years, until mining operations were moved to Ruby Mountain in 1982, this was the site of the worldâ&#x20AC;&#x2122;s oldest continuously operating garnet mine and the countryâ&#x20AC;&#x2122;s second oldest continuously operating mine under one management. The community at the mine site was the highest self-sufficient community in New York State, capable of housing about 11 families and supplied with its own water, power, and fire protection. The 16 km company-built road from NY State Route 28 rises 91 m per mile and, like other roads in the vicinity, was surfaced with coarse mine tailings. Currently extant on the property are residences, some of the original mine buildings, and Highwinds, built by Mr. C.R. Barton in 1933 as a family residence (Figure 2).

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Figure 2: Barton Mine at the summit of Gore Mountain looking west to east, 1956. Mine buildings center foreground, waste piles, foreground, residences in trees, center. Photo courtesy of the Adirondack Museum.

The early history of the Barton garnet mine has been compiled by Moran (1956) and is paraphrased here from that source. Mr. Henry Hudson Barton came to Boston from England in 1846 and worked as an apprentice to a Boston jeweler. While working there in the 1850’s, Barton learned of a large deposit of garnet located in the Adirondack Mountains. Subsequently, he moved to Philadelphia and married the daughter of a sandpaper manufacturer. Combining his knowledge of gem minerals and abrasives, he concluded that garnet would produce better quality sandpaper than that which was currently available. He was able to locate the source of the Adirondack garnet stones displayed at the Boston jewelry store years before. Barton procured samples of this garnet, which he pulverized and graded. He then produced his first garnet-coated abrasive by hand which was tested in several woodworking shops near Philadelphia. It proved to be a superior product and Barton soon sold all he could produce. H.H. Barton began mining at Gore Mountain in 1878 and in 1887 bought the entire mountain from the State of New York. Early mining operations were entirely manual. The garnet crystals in Barton’s mine were commonly 30 cm in diameter and rarely up to 1 m with an average diameter of 9 cm (Hight 1983). The garnet was hand cobbed (i.e., separated from the waste rock by small picking hammers and chisels). Due to the obstacles in moving the ore, the garnet was mined during the summer and stored on the mountain until winter. It was then taken by sled to the railroad siding at North Creek, whence it was shipped to the Barton Sandpaper plant in Philadelphia for processing. The “modern” plant at Gore Mountain was constructed in 1924. Crushing, milling, and coarse grading was done at the mine site. In 1983, the Gore VOLUME 21

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Mountain mining operation closed and mining was relocated to the Ruby Mountain site, approximately 6 km northeast, were it continues at present. The mine at Gore Mountain is approximately 2 km in length in an ENE-WSW direction. The ore body varies from 15 m to 122 m and is roughly vertical. Mining was conducted in benches of 9 m using standard drilling and blasting techniques (Figure 3). The ore was processed through jaw and gyratory crushers to liberate the garnet and then concentrated in the mill on Gore Mountain. Garnet concentrate was further processed in a separate mill in North River at the base of the mountain. Separation of garnet was and is accomplished by a combination of concentrating methods including heavy media, magnetic, flotation, screening, tabling, and air and water separation. Processes are interconnected and continuous or semi-continuous until a concentrate of 98% minimum garnet for all grades is achieved (Hight 1983). Finished product ranges from 0.6 cm to 0.25 micron in size. Figure 3: West end of Barton Mine, c. 1995. Ore here is garnet amphibolite. Note people, left center, for scale. Photo by author.

Garnet in general is used in waterjet cutting (35%), abrasive blasting (30%), water filtration (20%), abrasive powders (10%), and other processes (5%) (Olson 2013) such as to remove the red hulls from peanuts and as an anti-skid additive to aircraft carrier deck paint. Garnet is non-toxic, lacking crystalline silica, and is chemically inert, and it provides greater cutting speed, less dust, and lower volume requirements than competing abrasives. Overall, however, garnet comprises only a small portion (~2%) of the abrasives market. The garnet mined at Gore Mountain was a very high-quality abrasive. Although garnet does not normally exhibit cleavage, the garnets from Gore Mountain and those from the

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surrounding region exhibit a tectonically induced “pseudo-cleavage” that produces sharp, angular fragments and greatly enhances the cutting ability of the final product (Figure 4). Present at a macro scale, this pseudo-cleavage is exhibited in all of Barton’s products. The markets currently served by Barton Mines Co. LLC are, in decreasing order, waterjet cutting, glass lapping, finishes, and abrasive coatings. Abrasive air blasting and water filtration media are minor. The value of garnet varies widely depending on a number of factors from $75 to $325 per ton (Olson 2015). Barton’s products fall into the upper price range. Figure 4: Tectonically induced “pseudo-cleavage” in Gore Mountain garnet. This fracture pattern is present to 0.25 micron scale. Photo by Bruce Selleck.

Although the garnet crystals in the ore zone at Gore Mountain are atypical in size, the modal amount of garnet is not unusually high for Adirondack garnet amphibolites. Garnet amphibolite that is texturally and mineralogically similar occurs elsewhere in the Adirondacks, usually on the margins of gabbroic rock bodies. The ore at the currently operating Barton Corporation mine at Ruby Mountain, for example, is of the same tenor, but the garnets rarely are larger than 2.5 to 5 cm (Figure 5). The composition of the garnet at Gore Mountain is roughly 43% pyrope, 40% almandine, 14% grossular, 2% andradite, and 1% spessartine (Levin 1950; Harben and Bates 1990). Chemical zoning, where present, is very weak and variable (Luther 1976). The garnet has been so well analyzed isotopically that it is frequently used as an 18O/16O standard (Valley et al. 1995). Typical chemical analyses of the garnet are presented in Table 1. Hardness of the garnet is 7.5 and the average density is 3.95 gm/cm3. VOLUME 21

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Figure 5: Garnet ore (garnet amphibolite) at Barton’s Ruby Mountain mine. Knife – four inches. Photo by author.

Table 1: Electron Microprobe analyses of Gore Mt. garnet (almandine-pyrope) normalized to 8 cations and 12 anions (Kelly and Petersen 1993). *Calculated by charge balance.

OXIDE WEIGHT PERCENT

#29

#41

SiO2

39.43

39.58

Al2O3

21.40

21.20

TiO2

0.05

0.10

FeO*

22.80

24.45

Fe2O3*

1.44

0.72

MgO

10.65

9.60

MnO

0.48

0.74

CaO

3.85

3.97

Na2O

0.00

K2O

0.00

Total

100.09

100.36

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Gore Mountain garnet hosts a number of inclusion types, the most common of which is acicular rutile. Other common solid inclusions include pyrite, plagioclase, pyroxene, hornblende, ilmenite, apatite, and biotite (Valley et al. 1995). Garnet has been legislatively designated as the official New York State gemstone. Barton Mines LLC itself produces no gem material but collectors are able to find rough material of gem quality. Stones cut from Gore Mountain rough material generally fall into a range of one to five carats. A small number of stones displaying asterism have been found. Many included rutile needles that are crystallographically controlled, and the asterated specimens may be due to the orientation of these inclusions parallel to {111} of the garnet (Figure 6). Garnets from this locality are a dark red color with a slight brownish tint. Special cutting schemes have been devised for this material in order to allow sufficient light into the stone. Figure 6: Crystallographically-controlled rutile needles in garnet which impart asterism to faceted garnet gemstones. The field of view for the star garnet image is 3.25 mm wide. Photo by R. Darling.

GEOLOGY The garnet mine is entirely hosted by a hornblende-rich garnet amphibolite unit along the southern margin of an olivine meta-gabbro body (Figure 7). The garnet amphibolite grades into garnet-bearing gabbroic meta-anorthosite to the east. To the south, the garnet amphibolite is in contact with charnockite; a fault forms this southern contact. The ore zone is a granulite facies lithology with a relict subophitic texture. Preserved igneous

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features, faint igneous layering, and a xenolith of anorthosite have been reported in the meta-gabbro (Luther 1976). Prior to metamorphism, the rock was composed of plagioclase, olivine, clinopyroxene, and ilmenite. During metamorphism, coronas of orthopyroxene, clinopyroxene and garnet formed between the olivine and the plagioclase and coronas of biotite, hornblende, and ilmenite formed between plagioclase and ilmenite (Whitney and McLelland 1973, 1983). The contact between the olivine meta-gabbro and the garnet amphibolite ore zone is gradational through a narrow (1 to 3 m wide) transition zone. Garnet size increases dramatically across the transition zone from less than 1 mm in the olivine meta-gabbro, to 3 mm in the transition zone, to 5 to 35 cm in the amphibolite (Goldblum and Hill 1992). This increase in garnet size coincides with a ten-fold increase in the size of hornblende and biotite, the disappearance of olivine, a decrease in modal clinopyroxene as it is replaced by hornblende, and a change from green spinel-included plagioclase to white inclusion-free plagioclase (Goldblum and Hill 1992). Mineralogy in the garnet amphibolite ore zone is mainly hornblende, plagioclase and garnet with minor biotite, orthopyroxene, and various trace minerals. In both the olivine meta-gabbro and the garnet amphibolite, garnet content averages 13 modal percent, with a range of 5 to 20 modal percent (Luther 1976; Hight 1983; Goldblum 1988). Figure 7: Geologic map of Barton garnet mine and surrounding area. The ore zone is megagarnet amphibolite. From McLelland and Selleck (2011).

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The garnet amphibolite unit is thought to be derived by granulite facies metamorphism of the southern margin of the olivine meta-gabbro. At the west end of the mine, a garnet hornblendite with little or no feldspar is locally present. This rock may represent original ultramafic layers in the gabbro (Whitney et al. 1989). In the more mafic portions of the ore body, the large garnet crystals are rimmed by hornblende up to several centimeters thick. Elsewhere, in less mafic ore, the rims contain plagioclase and orthopyroxene. Chemical analyses of the olivine meta-gabbro and garnet amphibolite show that the garnet ore was derived by isochemical metamorphism, except for an increase in the H2O and f O2 of the olivine meta-gabbro (Table 2; Luther 1976). Very coarsely approximated, the reaction olivine + plagioclase + (clinopyroxene + ilmenite) + fluid â&#x2020;&#x2019; garnet + hornblende + (less calcic plagioclase + orthopyroxene + biotite) occurred during the formation of the ore body.

Table 2: Chemical analyses of olivine metagabbro and garnet amphibolite (ore), Gore Mountain (Luther 1976).

OLIVINE METAGABBRO

GARNET AMPHIBOLITE

SiO2

47.14

45.68

Al2O3

16.98

17.32

TiO2

0.18

0.78

Fe2O3

0.69

1.30

FeO

11.13

9.67

MnO

0.16

0.15

MgO

11.04

10.97

CaO

8.05

8.58

Na2O

2.54

2.85

K2O

0.56

0.59

P2O5

0.01

0.10

H2O

0.44

1.16

Total

99.64

99.15

A strong, consistent lineation and weak planar fabric coincide with the zone of large garnet crystals and are an important feature of the garnet ore zone (Goldblum and Hill 1992). The lineation is defined by parallel alignment of prismatic hornblende crystals, elongate segregations of felsic and mafic minerals, plagioclase pressure shadows, and rare elongate garnet. The foliation is defined by a slight flattening of the felsic and mafic aggregates.

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Darling et al. (1997) report a most unusual type of multiple solid inclusion containing the low pressure, very high temperature SiO2 polymorph, cristobalite. This phase is accompanied by albite and a small quantity of ilmenite. The cristobalite is recognized by its fractures, formed by the 5% volume decrease upon a phase transformation occurring at temperatures between 260 and 270 Â°C. Darling et al. (1997) propose the cristobalite + albite + ilmenite inclusions began as small water-rich melt inclusions which then experienced diffusive loss of water. This led to an internal pressure decrease (under nearly isochoric, isothermal conditions) to the point where cristobalite, instead of quartz, crystallized in the melt inclusions. It should be noted that identical cristobalite-bearing multiple-solid inclusions also occur in garnet amphibolites at the former Hooper and North River Mines (Charles et al. 1998), so their formation is not unique to Barton Mine garnet. The most remarkable outcome is that the cristobalite never reconstructively transformed to quartz even during protracted cooling from starting conditions of approximately 800 Â°C. Darling et al. (1997) infer the absence of water was the primary reason for the preservation of cristobalite. Fluid inclusions are rare in Gore Mountain garnet despite the importance of water in the formation of garnet amphibolite as well as large crystal sizes. Ironically, the most common fluid inclusion in Gore Mountain garnet is CO2-rich and is texturally secondary. These inclusions, like those in many other Adirondack rocks, most likely formed along the retrograde path following peak metamorphic conditions. Precisely how CO2-rich inclusions can form in garnet (or more commonly quartz) is unknown as neither mineral is soluble in liquid CO2. Two possible explanations include: 1) low temperature mineral growth from the aqueous portion of an immiscible H2O-CO2 fluid while trapping CO2, or 2) diffusive loss of H2O from an original mixed H2O-CO2 inclusion.

GEOLOGIC HISTORY Petrologic studies (Buddington 1939, 1952; Bartholome 1956, 1960; Luther 1976; Sharga 1986; Goldblum 1988; Goldblum and Hill 1992; McLelland and Selleck 2011) have concluded that the growth of the large garnets is related to a localized influx of water along the margin of the granulite facies olivine meta-gabbro body. The Gore Mountain garnets are chemically homogeneous suggesting that a) the garnets grew under conditions in which all chemical components were continuously available, and b) the temperature and pressure conditions were uniform during the period of garnet formation. A zone of high fH2O along the southern margin of the original gabbro body may have enhanced diffusion and favored growth of very large garnets and thick hornblende rims at the expense of plagioclase and pyroxene. Luther (1976) speculates that physical and chemical conditions were favorable for the growth of garnet but poor for the nucleation of garnet so that the garnet crystals that did nucleate grew to large size. The presence of hydrothermal fluids provides a steady supply of chemical components promoting the growth of large crystals.

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Newton and Manning (2008, 2010) have shown that the transport of Al2O3 necessary to form garnet is greatly enhanced by hot, saline fluids under the peak metamorphic conditions of the Adirondacks (8 kbar, 800 °C). McLelland (2002) demonstrated the presence of saline fluid inclusions in the rocks involved. Recognition that the garnet ore body and deformation fabric coincide with the southern margin of the olivine meta-gabbro body led Goldblum and Hill (1992) to hypothesize that the high fluid flow required for growth of large garnet crystals was the result of ductility contrast at a lithologic contact during high-temperature shear zone deformation. The olivine meta-gabbro is a granulite facies rock with a poorly developed foliation and little evidence of ductile deformation. In the transition zone between the olivine meta-gabbro and the garnet amphibolite, increased ductile deformation resulted in grain-size reduction of plagioclase and pyroxene. Microstructures in plagioclase in the transition zone indicate plastic deformation, and the concurrent modal increase in hornblende indicates an influx of fluid. Fabric development and hydration are most apparent in the garnet amphibolite of the ore zone. According to Goldblum and Hill (1992), the olivine meta-gabbro remained competent and initially deformed by brittle processes along its southern margin, while the adjacent feldsparrich charnockite and gabbroic meta-anorthosite deformed by ductile processes during deformation at amphibolite facies conditions. Initial grain-size reduction by cataclasis along the margin of the meta-gabbro allowed hydration and metamorphism to produce the garnet amphibolite. During metamorphism, the garnet amphibolite was likely a high-strain zone of reaction-enhance ductility. Eventually, metamorphic reactions apparently outpaced the rate of deformation and grain coarsening impeded ductile deformation processes (Goldblum and Hill 1992). It is not currently possible to specify the ultimate origin of the hydrothermal fluids responsible for the growth of garnet megacrysts at Gore Mountain and elsewhere in the Adirondacks, although a mantle source is possible. However, the formation of the garnets has been dated at 1059 ± 19 Ma (Basu et al. 1989), 1051 ± 4 Ma (Mezger et al. 1992), and 1046.6 ± 6 Ma (Connelly 2006). McLelland and Selleck (2011) conclude, based upon an average of previous dates, that the garnets formed at 1049 ± 5 Ma. The youngest major intrusive rock in the Adirondacks is the abundantly distributed Lyon Mountain Granite, which is reliably dated at 1049 ± 10 Ma (McLelland et al. 2010). Numerous pegmatites, granite dikes, and quartz veins, generally undeformed, are intrusive into all other lithologies. The average age of these pegmatitic rocks falls at the younger end of the range of ages available for the Lyon Mountain Granite. McLelland and Selleck (2011) conclude that the pegmatite represents the termination of the intrusion of the Lyon Mountain Granite. Pegmatite occurs at Gore Mountain in the fault contact between the garnet ore zone and the charnockite to the south. Therefore, it is probable that megacrysts of garnet, such as those found at Gore Mountain and elsewhere in the Adirondacks, are the result of the reaction between hydrothermal fluids and upper

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amphibolite-grade gabbroic rock. The fluids were derived from the Lyon Mountain Granite or pegmatite derived therefrom and achieved access to the gabbroic rocks through steeply dipping faults or ductile shear zones. ACKNOWLEDGEMENTS

Portions of this article were published in “Geology and mining history or the Barton garnet Mine, Gore Mt. and the NL ilmenite mine, Tahawus, NY and a review of the MacIntyre iron plantation of 1857,” in the New York Geologic Association Fieldtrip Guidebook (William Kelly and Robert Darling 2009: 105-121) from the 80th Annual Meeting. Review of the article by Bruce Selleck is gratefully acknowledged. L I T E R AT U R E C I T E D

Basu, A.R., B.E. Faggart, and M. Sharma. 1989. “Implications of Nd-isotopic study of Proterozoic garnet amphibolites and wollastonite skarns from the Adirondack Mountains,” International Geologic Congress, 28(I): 95-96. Bartholome, P.M. 1956. Structural and petrologic studies in Hamilton County, NY. Unpublished Ph.D. thesis, Princeton University, 188 pp. Bartholome, P.M. 1960. “Genesis of the Gore Mt. garnet deposit, New York,” Economic Geology, 55(2): 255-277. Buddington, A.F. 1939. “Adirondack igneous rocks and their metamorphism,” Geological Society of America Memoir, 7, 295 pp. Buddington, A.F. 1952. “Chemical petrology of metamorphosed Adirondack gabbroic, syenitic, and quartz syenitic rocks, New York,” American Journal of Science, Bowen Volume: 37-84. Charles, M.A., J.J. Gordon, Jr., P.J. Walter, and R.S. Darling. 1998. “More cristobalite in Adirondack garnet,” Geological Society of America, Abstracts with Programs, 30: 10. Connelly, J.N. 2006. “Improved dissolution and chemical methods for Lu-Hf chronometry,” Geochemistry, Geophysics, Geosystems, 7. Q04005, 9, doi: 10.1029/2005GC001082. Darling, R.S., I-M Chou, and R.J. Bodnar. 1997. “An occurrence of metastable cristobalite in high pressure garnet granulite,” Science, 276: 91-93. Goldblum, D.R.. 1988. The role of ductile deformation in the formation of large garnet on Gore Mountain, southeastern Adirondacks. Unpublished M.A. thesis, Temple University, 108 pp.

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Goldblum, D.R. and M.L. Hill. 1992. “Enhanced fluid flow resulting from competency contrasts within a shear zone: the garnet zone at Gore Mountain, NY,” Journal of Geology, 100: 776-782. Harben, P.W. and R.L. Bates. 1990. “Garnet,” in Industrial Minerals: Geology and World Deposits, Metal Bulletin Plc., London, 120-121. Hight, R.P. 1983. “Abrasives,” in Industrial Minerals and Rocks, S.J., LeFond (Ed.), I (5), Society of Mining Engineers of the American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., 11-32. Kelly, W.M., and Petersen, E.U., 1993, Garnet ore at Gore Mountain, NY: in Selected Mineral Deposits of Vermont and the Adirondack Mountains, E. U. Peterson, ed., Soc. Econ. Geol. Guidebook Series, v. 17, 1-9. Levin, S., 1950, Genesis of some Adirondack garnet deposits: Geological Society of America Bulletin v.61, 516-565. Luther, F.R., 1976, The petrologic evolution of the garnet deposit at Gore Mountain, Warren County, NY: Unpublished. Ph. D. Thesis, Lehigh University, 224 pp. McLelland, J.M., J. Morrison, B.W. Selleck, B. Cunningham, and C. Olson. 2002. “Hightemperature hydrothermal alteration of late- to post-tectonic Lyon Mountain Granitic Gneiss, Adirondack Highlands, New York: Origin of quartz-sillimanite nodules, quartz-albite facies and associated low-Ti, Fe oxide Kiruna-type deposits,” Journal of Metamorphic Petrology, 20: 175-190. DOI: 10.1046/j.0263-4929.2001.00345.x. McLelland, J.M., B.W. Selleck, and M. Bickford. 2010. “Review of the Proterozoic evolution of the Grenville Province, its Adirondack outlier and, and the Mesoproterozoic inliers of the Appalachians,” in R. Tollo et al. (Eds.), From Rodinia to Pangaea: The lithotectonic record of the Appalachian region. Geological Society of America Memoir, 206: 1-30. DOI:10.1130/2010.1206(02). McLelland, J.M. and B.W. Selleck. 2011. “Megacrystic Gore Mountain-type garnets in the Adirondack Highlands, origin and tectonic implications,” Geosphere, 7(5): 1194-1208. Mezger, K., E. Essene, and Halliday. 1992. “Closure temperatures of the Sm---Nd system in metamorphic garnets,” Earth and Planetary Letters, 113: 397-409. Moran, R. 1956. “Garnet Abrasives: An 80 year history of the Barton Mines Corporation,” Business Biographies, 47 pp. Newton, R., and C. Manning. 2008. “Stability of corundum in the system Al2O3-SiO2H2O-NaCl at 800 °C and 10 kbar,” Chemical Geology, 249: 250-261. DOI: 10.1016/j. chemgeo.2008.01.002.

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Newton, R., and C. Manning. 2010. “Role of saline fluids in deep crustal and upper mantle metasomatism: Insights from experimental studies,” Geofluids, 10: 58-72. Olson, D.W. 2015. “Garnet, industrial,” Mineral Commodities Summaries. Accessed January 2016 from http://minerals.usgs.gov/minerals/pubs/commodity/garnet/mcs-2015-garne.pdf. Olson, D.W. 2013. Garnet, industrial, advanced release. USGS 2012 Minerals Yearbook Vol. 1: Metals and Materials. Accessed January 2016 from http://minerals.usgs.gov/minerals/ pubs/commodity/garnet/myb1-2013-garne.pdf. Sharga, P.J. 1986. Petrologic and structural history of the lineated garnetiferous gneiss, Gore Mountain, New York. Unpublished M.S. thesis, Lehigh University, 224 pp. Valley, J.W., N. Kitchen, M.J. Kohn, C.R. Niendorf, and M.J. Spicuzza. 1995. “UWG-2, a garnet standard for oxygen isotope ratios” Strategies for high precision and accuracy with laser heating,” Geochemical et Cosmochimica Acta, 59: 5223-5231. Whitney, P.R. and J.M. McLelland. 1973. “Origin of coronas in metagabbros of the Adirondack Mountains,” Contributions to Mineralogy and Petrology, 39: 81-98. Whitney, P.R. and J.M. McLelland. 1983. “Origin of biotite-hornblende-garnet coronas between oxides and plagioclase in olivine metagabbros, Adirondack region, NY,” Contributions to Mineralogy and Petrology, 82: 34-41. Whitney, P.R., S.R. Bohlen, J.D. Carl, W. deLorraine, Y.W. Isachsen, J.D. McLelland, J.F. Olmsted, and J.W. Valley. 1989. The Adirondack Mountains - a section of deep Proterozoic crust. 28th International Geological Congress Field Trip Guidebook T164, American Geophysical Union, Washington, D.C., 63 pp.

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FAULTS AND FRACTURE SYSTEMS IN THE BASEMENT ROCKS OF THE ADIRONDACK MOUNTAINS, NEW YORK DAVID W. VALENTINO, 1 JOSHUA D. VALENTINO, 2 JEFFREY R. CHIARENZELLI, 3 AND RICHARD W. INCLIMA 1

1. State University of New York at Oswego, Oswego, NY 13126 2. Department of Geosciences, Virginia Tech, Blacksburg, VA 24061 3. Department of Geology, St. Lawrence University, Canton, NY 13617

KEYWORDS:

Faults, Fractures, Brittle Structures, Post-Grenville Tectonic History, Piseco Lake Graben, Prospect Fault

INTRODUCTION While significant progress has been made in our understanding of the Mesoproterozic geologic history of the Adirondack Mountains (Figure 1) and the entire Grenville Province (Chiarenzelli et al. 2011; McLelland et al. 2010; Rivers 2008), relatively little research has been completed on the late, brittle geologic structures since the 1980s (Isachsen and McKendree 1977; Isachsen et al. 1983; Isachsen 1985; Weiner and Isachsen 1987). The Adirondack Mountains (Figure 1) have a distinct, north-northeast and east-northeast trending topographic grain (Figure 2) related to this later brittle history. These fracture systems and faults overprint a region largely shaped by deep-crustal, ductile processes (Gates et al. 2004; McLelland 1984). Fundamental questions regarding the age, origin, and kinematic history of these fracture systems and faults, their influence on the adjacent Paleozoic basins, and their potential for generating earthquakes remain largely unknown and/or loosely constrained. This article is a general introduction to the types of brittle geologic structures found in the Adirondack Mountains rather than a complete summary of all brittle features in the region. Most of the examples described in this article are in areas that are readily accessible.

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FAULTS, FRACTURE SYSTEMS, AND GRABEN

Lineaments The landscape of the Adirondacks is dominated by long (10s of kilometers [km]) northeast trending linear valleys (e.g., the valleys containing Long Lake, Indian Lake, Piseco Lake, and the northeast arm of the Great Sacandaga Reservoir; Figure 2). The northeast trending lineaments cross cut geologic (rock type) contacts, and it has been argued that the linear persistence of these valleys is due to differential erosion along prominent fracture systems and fault zones (Isachsen and McKendree 1977; Isachsen et al. 1983). These prominent northeast trending topographic features (Figure 2) are dissected by several other lineament sets that trend east-northeast, northwest, east-west, and a minor north-south trending population. The northwest trending lineaments are persistent in the southeastern and northwestern regions of the Adirondacks, where they are nearly parallel to (southeast trending) and cross cut (northwest trending) the Proterozoic geologic structures defined by bedrock mapping. The east-northeast and east-west lineaments are parallel to Proterozoic structure in the southern Adirondacks (south of Piseco Lake), where they form broad arcuate geomorphic discontinuities (Fakundiny 1986), but they also cross cut Proterozoic structures in the central Adirondacks. The minor north-south trending lineaments are significantly shorter than the others and are most likely associated with the Pleistocene glacial history of the Adirondacks. Figure 1: Map showing the location of the Adirondack Mountains with respect to the northeast U.S. and Canada.

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Figure 2: Digital elevation model of the Adirondack Mountains region with topographic lineaments showing the strong correlation between the landscape and geologic structures.

Fault Map The Preliminary Brittle Structures Map of New York (Isachsen and McKendree 1977) illustrates the distribution and general attitude of faults in the Adirondack Mountains (Figure 3). With the exception of a few faults that trace east-west across the central and southern Adirondacks, the region is dominated by northeast striking faults that displace geologic contacts. These northeast-striking faults are mainly normal faults. There are numerous northeast striking normal faults in the eastern half of the Adirondacks Mountains. Within this region, two fault networks cross the entire dome from northeast-southwest. An anastomosing network of normal faults traces more than 150 km from area of Dolgeville, north through Piseco and Indian Lakes, and the high peaks area of Lake Placid. A parallel network of faults trace from Gloversville in the southwest through North Creek and Schroon Lake in the northeast. VOLUME 21

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Detailed geologic mapping in the vicinity of Indian Lake (de Waard and Romey 1969; Gates et al. 2004; Valentino et al. 2004), paired with documentation of fracture systems and magnetic anomaly profile modeling (Kush et al. 2006; Mantaro and Valentino 2007), shows that the contacts between metaplutonic and metasedimentary rocks, and metamorphic foliation in the Proterozoic rocks, are truncated by a normal fault system. However, magnetic anomalies mapped on Indian Lake suggest a component of sinistral (left-lateral, near-horizontal) offset (Valentino et al. 2012). Farther south, the axis of the Proterozoic Piseco antiform is similarly displaced by sinistral offset at Piseco Lake (Valentino et al. 2012).

Fault and fracture system characteristics As recognized by earlier researchers, there are few places in the Adirondack Mountains where brittle faults are exposed due to concealment in deep valleys filled with glacial sediments and colluvium, and lakes. Adirondack fault systems are made up of many small faults and fracture zones, which weather to weak, easily eroded rock, and thus hamper our ability to find natural exposures. However, there are some excellent locations where faults, related features, and fracture systems can be examined in the field, specifically on water washed and ice polished rock islands in lakes and the abundant cuts that were made during the construction of the roads in the Adirondacks. Three example locations will be described here: 1) small (<20 m) rock islands at Indian Lake; 2) the Piseco Lake area; and 3) road cuts on Route 8 near Hoffmeister, NY.

Figure 3: Fault map for the Adirondack Mountains (after Isachsen and McKendree 1997). GSR-Great Scandaga Reservoir; HL-Hinkley Lake; IL- Indian Lake; LG-Lake George; LL- Long Lake; PL-Piseco Lake. Earthquake epicenters are represented by the green circles with size depicting the magnitude (data compiled from the USGS Earthquake Archive 2016).

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Indian Lake fault zone A Proterozoic structural dome occurs in the region of Snowy Mountain, immediately west of Indian Lake (de Waard and Romey 1969; Gates et al. 2004; Valentino and Chiarenzelli 2008). The dome is defined by penetrative S-L tectonite developed in gabbroic- and charnockiticgneisses that surround a core of moderately deformed megacrystic anorthosite. The dome is flanked by metasedimentary belt of rock containing interlayered quartzite, marble, calc-silicate, and pelitic gneiss (deWaard and Romey 1969; Gates et al. 2004). This dome is truncated by the fault zone that occurs beneath Indian Lake (Figure 4), and displacement estimates based on modeling magnetic anomaly data suggest oblique displacement with the vertical component of about 1 km and the horizontal sinistral component of about 2 km (Mantaro and Valentino 2007; Valentino et al. 2012). Well-developed meter-scale zones containing northeast striking, subvertical anastomosing shear fracture (spacing <10 centimeters [cm]) occur in the rock islands at Indian Lake (Kush et al. 2006) composed of charnockitic gneiss (Figure 5A). Faulted, ground up rock (gouge) within these zones consists of broken grains of plagioclase, K-feldspar, quartz, and gash fractures filled with quartz and chlorite (Figure 5B). Detailed fracture maps reveal a network of nearly orthogonal fracture systems south of Indian Lake, where it appears that the main fault zone splays and underlies the southern arms of the lake. Northeast striking shear fractures are most prevalent, and where there are adequate markers, they appear to have experienced sinistral slip. On the contrary, the northwest striking fracture set is less developed and they display dextral (right-lateral, near-horizontal) shear. Based on this information, Valentino et al. (2012) conclude that the northwest striking fractures accommodated counterclockwise rotation of blocks between two fault splays that experienced sinistral offset (Figure 6). The Indian Lake fault zone can be traced using lineaments for many kilometers to the northeast and to the southwest of the lake region. Following the lineaments to the southwest, it appears that the fault zone has displaced formation contacts in the area north of Speculator, NY. Continuing farther southwest, the fault zone enters the broad valley of Piseco Lake (Figure 7). Cannon (1937) mapped several steep dipping normal faults in this region based on the offset of geologic contacts and correlation with lineaments. At Piseco Lake, the axis of a Proterozoic antiform defined by metamorphic foliation is clearly offset about 2 km, with the shear sense sinistral but most likely also having a normal component. Fractures were mapped in the regions adjacent to Piseco Lake, and they have a similar orientation to those observed to the northeast (Valentino et al. 2012). It is rare to find natural exposures of the fault rocks in the back country of the Adirondack Mountains because they readily weather due to abundant fracture porosity. However, excellent road cuts immediately south of Piseco Lake display zones of intense fracturing that may represent minor splays off of the main fault zone. One such exposure is a fine example of the variability of developed fractures (Figure 8). Most commonly, the bedrock within and near the fault zones has a fracture spacing ranging from 0.5 to 1 m, but within the fracture zones, the frequency of fractures can be greater than 25 over a distance of less than a meter (spacing <4 cm). Typically, these fracture zones range from a few meters to more than 10 m wide, with transition zones on either side where fracture density gradually increases when traversing from outside to inside the zone.

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Figure 4: Fault and fracture map for the southern Indian Lake region.

Piseco Lake â&#x20AC;&#x201C; Propect fault zone The Indian Lake fault zone intersects the Prospect fault zone in the area immediately southwest of Piseco Lake. Unlike most major faults in the Adirondacks, the Prospect fault cuts across the region with a generally east-west strike, forming a broad arcuate trace, essentially following the ductile structure of the region (Figure 2). Like the other faults, there are few places where the Prospect fault can be observed in outcrop. But it does occur in the bed of the West Canada Creek in the lower reaches of the Ohio Gorge and can be directly observed during times of very low discharge. Within the gorge, the fault is characterized by roughly east-west striking anastomosing shear fractures with narrow (<1 m) breccia and gouge domains developed from the local granitic gneiss. Rare brittle shear sense indicators suggest complex displacement on the Prospect fault with some showing normal shear and other exhibiting strike-slip. A prevalent fracture set that is subparallel to the fault occurs throughout the region of the fault but also in the western Adirondacks in general (Figure 9). The Prospect fault zone is shown on the New York State geologic map to trace westward through Hinkley Lake, where it exits the Adirondack basement and has displaced the Ordovician carbonates of the Trenton Group. A strong linear magnetic anomaly that occurs at Hinkley Lake was interpreted to be the trace of the fault (Hewitt et al. 2009; Valentino et al. 2012).

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Hoffmeister area Outcrops along Route 8 in the west-central Adirondacks contain well developed fault breccia derived from the local granitic gneiss. One of the best examples occurs in an exposure located east of Hoffmeister, NY. At this location the breccia occurs in irregular domains that are upward of 5 m wide. The breccia is defined by variable sized fragments of grantic gneiss with a fine-grained matrix of green chlorite and grains of quartz and feldspar (Figure 10). This breccia occurs where the Prospect Fault appears to be intersected by one of the northeast striking splays associated with the Indian Lake Fault. The lack of breccia exposure beyond the road cut makes it difficult to determine if it is developed in one or both faults. Regardless, this breccia has the typical texture and secondary mineralogy that is observed in most Adirondack faults.

Graben Structures There are several graben associated with the northeast striking faults. Some of these graben contain Paleozoic strata, indicating that the Adirondack basement was once overlain by Cambrian and Ordovician sedimentary rocks (Isachsen and Fisher 1970; Isachsen and McKendree 1977). Some grabens are filled with Quaternary sedimentary deposits, and others appear to be concealed by modern wetlands and lakes. The graben at Wells, NY (Figure 11) is one of the best exposed and well-known structures in the south-central Adirondacks. The Wells Outlier contains Cambrian sandstones and dolomites, as well as upper Ordovician carbonates and shale, in a down-faulted block approximately 2 km wide and 7 km long, with minimum normal displacement of 1000 m (Miller 1916). The western border fault is projected to the southwest, where it ends in the Mohawk River valley. The northeastern extension of the fault follows the East Branch Sacandaga River and cuts across the Orogen dome. Breccia that is several tens of meters wide is well developed in this fault, and local fractures are subparallel to the zone of fault breccia. The valley of Piseco Lake was proposed to be a graben (Cannon 1937) bordered by fault splays linked to the Indian Lake fault zone. An integrated structural geology and magnetic gradiometry analysis was completed to develop a geometric and kinematic model for a proposed graben (Valentino et al. 2012). A series of linear magnetic anomalies in Piseco Lake are parallel to the local topographic northeast trending lineaments and subparallel to the dominant fractures that occur in the bedrock immediately west of the lake. As reported by Valentino et al. (2012), magnetic model solutions require the addition of a rock body with a low negative susceptibility, indicating a rock body under the lake that is rich in either quartz or calcite, with Paleozoic carbonate strata as found in other Adirondack graben being the best candidate. It was concluded that Piseco Lake resides over a graben that developed as an oblique-sinistral pull-apart basin (Figure 7) with a throw large enough to preserve Paleozoic strata that once covered theÂ AdirondackÂ basement.

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Figure 5A: Outcrop photograph of charnockitic gneiss at Indian Lake, with thin breccia and gouge zones. Minor drag fold shows sinistral shear on northeast striking fracture.

Figure 5B: Photomicrograph of fault breccia from the Indian Lake fault zone at Indian Lake consisting of fragments of granitic gneiss in a fine grained matrix of chloritized granite gneiss gouge.

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TECTONIC IMPLICATIONS Jacobi and Mitchell (2002) proposed that the deposition of upper Ordovician strata in the Mohawk Valley, south of the Adirondack massif, was controlled by fault bounded structural blocks, demonstrating basement fault activity during Late Ordovician foreland basin development. These faults are the southern extension of major basement faults, such as the Indian Lake Fault Zone. On the western side of the Adirondack Mountains, Wallach and Rheault (2010) suggested that the gentle southwestern incline of the Ordovician strata is directly the result of basement faulting and uplift of the Adirondack dome. They further suggested that reactivation of a major basement shear zone (Carthage-Colton shear zone) and movement on other proposed basement faults based on lineament analysis contributed to the formation of the Tug Hill plateau. The eastern margin of the Adirondacks is bordered by major grabens that host Lake George and Lake Champlain. North of the Adirondacks there is a major fault system in the St. Lawrence River valley (Wallach 2002). Isachsen (1981) described the graben associated with the northeast striking Adirondack fault zones, clearly demonstrating that the Adirondack basement was once covered by Cambrian-Ordovician sedimentary rocks of the Appalachian basin. These basement faults likely served to accommodate the differential uplift of the region from 163 to 183 million years ago (Roden-Tice et al. 2000) â&#x20AC;&#x201C; uplift that is largely responsible for the current domeshaped topographic outline of the Adirondack Mountains region (Isachsen 1985). Taking into account the kinematic information recently documented for several Adirondack faults and the related fractures, it is possible that uplift was accommodated by both normal and sinistral (Figure 12) displacement (Valentino et al. 2012). Additionally, Isachsen (1975, 1981) proposed that Adirondack crust continues to rise, and this is partially supported by seismic activity on the Saint Lawrence fault zone and in the Champlain Valley (Barosh 1986, 1990, 1992; Faure et al. 1996; Mareschal and Zhu 1989; Wallach 2002). With a few exceptions, earthquakes that have occurred in the Adirondack Mountains were generally low magnitude (<4.0) and shallow (<5 km). Figure 3 shows the distribution of earthquake epicenters and magnitudes from 1973 to 2016 (data compiled from USGS Earthquake Archive). About 58% of the quakes had a magnitude of less than 2.0, with 40% ranging from 2.0 to less than 4.0 magnitude. Most earthquakes occurred in a broad north-south trending zone that extends from the central Adirondacks toward the St. Lawrence River. Despite the persistence of northeast striking lineaments and fault zones in the Adirondacks, Deneshfar and Ben (2002) concluded that northwest striking faults in the Adirondack Mountains are more likely to exhibit seismic activity. The largest recorded earthquakes in the Adirondack region occurred near Massena in 1944 (magnitude of 5.8), in the Plattsburgh area in 2002 (magnitude 5.3), and in the central Adirondacks in 1983 (magnitude 5.1). Using the first motion of the earthquake P-waves, the fault plane orientations (nodal planes) for the 1983 and 2002 earthquakes were resolved. Both earthquakes appear to be associated with shallowly dipping (<25 degrees), northnorthwest striking faults that do not break the earthâ&#x20AC;&#x2122;s surface, suggesting that both of these earthquakes developed under the current east-west directed intraplate tectonic stress. VOLUME 21

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Figure 6: Fracture trace map for the Indian Lake fault zone and the kinematic model based on shear fractures associated with the faults (after Valentino et al. 2012).

Figure 7: Magnetic anomaly map that as used to interpret faults under Piseco Lake. The inset rose diagram is a histogram depicting the strike of fracture data that was collected in the area immediately west of Piseco Lake (after Valentino et al. 2012).

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Figure 8: Outcrop photograph of a fracture zone located west of Piseco Lake. Fracture spacing in the fracture zone is about 4 cm, while the spacing is 50-100 cm for the remainder of the outcrop.

Figure 9: Digital elevation model for the central and southern Adirondacks and the transition into the Tug Hill plateau to the west. The contours depict the subsurface elevation for the top of the Trenton Group based on depths obtained from drilled wells. The contours show the gentle southwest tilt of the Paleozoic strata as the result of uplift in the Adirondack dome. Composite rose diagrams for five regions (A-E) in the basement show the strike of subvertical fracture systems.

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Figure 10: Outcrop photograph of brecciated granitic gneiss associated with the Prospect fault.

CONCLUSIONS 1. There are three general groups of topographic lineaments in the Adirondack Mountains with the major northeast trending lineaments being valleys that are underlain by fault zones. 2. The Indian Lake fault zone is one of the most extensive in the Adirondack Mountains, and it extends well beyond the Adirondacks into the Mohawk valley to the south and through the High Peaks region to the north. This fault zone consists of many splays with the total displacement that includes both normal and transcurrent displacement. 3. There are few fault zones that strike east-west in the central and southern Adirondack Mountains, but those that exist, such as the Prospect fault, are well-developed. These faults appear to cross-cut northeast striking faults, as in the area of Piseco Lake, where the Indian Lake fault zone intersects the Prospect fault. The Prospect Fault closely follows the trend of Mesoproterozoic ductile structure across the Adirondack Dome.

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4. There are three major steeply dipping fracture systems in the Adirondack Mountains associated with faulting. Northeast striking fractures are linked to the major northeast striking fault zones. Northwest striking fractures occur in structural blocks located between northeast striking faults. East-west striking faults have steeply dipping subparallel fractures. 5. The major northeast striking fault zones locally have associated graben structures, such as the grabens at Wells and Piseco Lake. These fault basins contain Paleozoic strata, providing firm evidence that the Adirondack dome was once covered by younger sedimentary rocks before uplift and erosion in the Mesozoic. As well, there is evidence that these graben developed as pull-apart basins during sinistral-normal shear. Figure 11: Simplified map of the graben at Wells, NY (after Isachsen and Fisher 1970).

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Figure 12: Structural model for the Adirondack basement to explain the occurrence of faults and three major fracture systems. PL denotes the location of the Piseco Lake graben.

ACKNOWLEDGEMENTS

The authors would like to thank Bruce Selleck for his careful review of our manuscript. We would also like to thank Rachel Lee for providing the high resolution photographs of outcrops used in this manuscript. L I T E R AT U R E C I T E D

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Roden-Tice, M.K., S.J. Tice, and I.S. Shofield. 2000. “Evidence for differential unroofing in the Adirondack Mountains, New York State, determined by apatite fission track termochronology,” Journal of Geology, 8: 155-169. United State Geological Survey, Earthquake Archive. Accessed 2016 from http://earthquake. usgs.gov/earthquakes/search. Valentino, D., J. Chiarenzelli, E. Hewitt, and D. Valentino. 2012. “Applications of water-based magnetic gradiometry to assess the geometry and displacement for concealed faults in the southern Adirondack Mountains, New York, U.S.A.,” Journal of Applied Geophysics, 76: 109-126. Valentino, D. and J. Chiarenzelli. 2008. “The southern Adirondack sinistral transpressive shear system,” Field trip guidebook of the Friends of the Grenville 37th Annual field meeting, 1-56. Wallach, J. 2002. “The presence, characteristics and earthquake implications of the St. Lawrence fault zone within and near Lake Ontario (Canada–USA),” Tectonophysics, 353: 45-74. Wallach, J. and M. Rheault. 2010. “Uplift of the Tug Hill Plateau in northern New York State,” Canadian Journal of Earth Science, 47: 1055-1077. Weiner, R.W. and Isachsen, Y.W. 1987. “Detailed studies of selected well-exposed fracture zones in the Adirondack Mountains dome,” New York, US Nuclear Regulatory Commission Technical Report (NUREG/CR-3232), 82 pp.

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WEATHERING NEAR THE SUMMIT OF HOUGH PEAK

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POST-VALLEY HEADS DEGLACATION OF THE ADIRONDACK MOUNTAINS AND ADJACENT LOWLANDS DAVID A. FRANZI, 1 JOHN C. RIDGE, 2 DONALD L. PAIR, 3 DAVID DESIMONE, 4 JOHN A. RAYBURN, 5 AND DAVID J. BARCLAY 6

1. Center for Earth and Environmental Science, SUNY Plattsburgh, 101 Broad Street, Plattsburgh, NY 12901, 518.564.4033, franzida@plattsburgh.edu 2. Department of Earth and Ocean Sciences, Tufts University, Lane Hall, Medford, MA 02155, 617.627.3494, Jack.Ridge@tufts.edu 3. Hanley Sustainability Institute and College of Arts and Sciences, University of Dayton, 300 College Park, Dayton, OH 45469, 937.229.3295, dpair1@udayton.edu 4. DeSimone Geoscience Investigations, Petersburg, NY 12138, 518.686.9809, djdesimone@gmail.com 5. Department of Geological Science, SUNY New Paltz, 1 Hawk Drive, New Paltz, NY 12561, 845.257.3767, rayburnj@newpaltz.edu 6. Department of Geology, SUNY Cortland, P.O. Box 2000, Cortland, NY 13045, 607.753.2921, david.barclay@cortland.edu

KEYWORDS:

Valley-Heads Deglaciation, Ontario – St. Lawrence and Champlain lowlands, Adirondack Uplands, Pleistocene

INTRODUCTION In the early 1900s, Herman LeRoy Fairchild (1909, 1912, 1919) developed a regional deglacial chronology for New York State in a series of New York State Museum Bulletins. Fairchild’s reports were accompanied by a collection of maps that encompassed the entire state at a scale of approximately 1:1,267,200 and depicted the locations of glacier ice, proglacial lakes and major rivers at different stages of ice recession. Fairchild’s

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work was published prior to the advent of radiocarbon dating techniques and did not have supporting numerical age control, but his synthesis was a masterful work and continues to be the most comprehensive treatment of deglacial history in New York. The regional deglacial chronology of the Adirondack region presented here is less ambitious in scale than Fairchildâ&#x20AC;&#x2122;s and was inspired by recent work on glacial stratigraphy in the lowlands peripheral to the Adirondack Upland (Figure 1). There is also now an improved understanding of the chronology of deglacial events in New York (Cronin, Rayburn, Guilbault, Thunell, and Franzi 2012; DeSimone et al. 2008; Franzi, Rayburn, Knuepfer, and Cronin 2007; Parent and Occhietti 1988; Rayburn, Cronin, Franzi, Knuepfer, and Willard 2011; Rayburn, Franzi, and Knuepfer 2007; Rayburn, Knuepfer, and Franzi 2005; Ridge 1997; Ridge, Brennan, and Muller 1990; Ridge, Franzi, and Muller 1991; Ridge and Franzi 1992; Stanford 2009) and New England that has been augmented by the North American Varve Chronology and radiocarbon ages (NAVC of Ridge 2016; Ridge et al. 2012); formerly the New England Varve Chronology (Antevs 1922, 1928; Ridge 2003, 2004) and paleomagnetic correlations (Ridge 2004; Ridge et al. 1990). Our intent is to summarize the current state of understanding of the style and chronology of deglaciation, identify areas where information is scarce or issues should be addressed, and encourage a new wave of scientific exploration and discovery in the Adirondack region. Figure 1: Physiographic regions of northeastern New York. The red stippled area is the Saranac Intramontane Basin (SIB; Buddington 1953).

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Regional Physiography The physiography of the Adirondack Upland and surrounding regions had a profound effect upon ice movements, patterns of ice recession, and the nature of glacial foreland and proglacial sedimentary environments during the last glacial maximum (LGM). The Adirondack Upland is a domal uplift about 250 km in diameter that is underlain predominantly by high-grade Mesoproterozoic metamorphic rocks (Figure 1) and surrounded by peripheral lowlands carved into lower Paleozoic sedimentary rocks. The High Peaks region contains 43 mountain peaks that lie above 1,219 meters (m) in elevation, including the highest summits in New York, Mt. Marcy (1,629 m) and Algonquin Peak (1,559 m). The region is characterized by rugged terrain where local relief may exceed 1,000 m (Cressey 1977). The High Peaks are surrounded by lower terrain in which many peaks, especially in the south-central highlands, exceed 600 m in elevation but generally local relief is less than 300 m. The Saranac Intramontane Basin (SIB; Buddington 1953) is an ovate, northeastâ&#x20AC;&#x201C;southwest trending structural basin bounded by low mountains, generally less than 800 m elevation that encompasses the headwaters of the upper Saranac, Salmon, St. Regis, and Raquette drainage basins. The region is characterized by the occurrence of many large lakes and well over a hundred smaller ponds that are developed in deposits of ice-contact stratified drift and glacial-fluvial outwash.

The Adirondack Mountains: Obstruction or Source of Glacial Ice An important question is how the Adirondack Upland influenced the regional pattern and timing of ice recession. Specifically, we shall address when and how the Adirondacks impeded regional ice flow and focused flow into lobes in adjacent lowlands. The lowland ice lobes impounded large proglacial lakes that drained in a succession of lowering levels, often punctuated by high-magnitude breakout floods, as lower outlets were uncovered with ice recession. The formation of ice lobes and the chronology of proglacial lake succession in adjacent lowlands was a central theme of Fairchildâ&#x20AC;&#x2122;s (1909, 1912, 1919) deglacial reconstructions. However, many of the lobes he envisioned had surface gradients that were too low to be realistic. Alternatively, the Laurentide Ice Sheet (LIS) may have overtopped parts of the Adirondacks and entered adjacent lowlands through much of the deglaciation history, especially from the southern and southwest Adirondacks into the Mohawk Valley. Our reconstructions address how the Adirondack Upland influenced the timing and pattern of ice recession in the region. The Adirondacks are critical in this regard because of their position at the transition between two glacial regimes with very different ice sheet dynamics. To the east is the rugged terrain of New England, not unlike the Adirondacks, that must have impeded ice flow and triggered a steeper ice sheet profile. This part of the LIS may have been more stable than areas to the west in regards to its sensitivity to climate events and glaciological changes, and it was minimally influenced by calving in glacial lakes. West of the Adirondacks, and in the surrounding lowlands, is the eastern limit of a Midwestern style

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of ice sheet that advanced across a smoother glacial bed and was floored by clayey sediment (e.g., Eyles and Doughty 2016). The ice sheet likely had faster flow, a gentler surface slope, and at times may have formed ice streams (Briner 2007; Hess 2009; Kerr and Eyles 2007). In these areas, the LIS was very sensitive to climate events and calving in large lakes and glacial readvances covered much greater distances. One may view the Adirondack region as one in which slow upland ice anchors the system and is forced to work in tandem with streaming lowland ice. An additional issue is whether or not local alpine glaciers occupied parts of the High Peaks following the retreat of the LIS. Early proponents of the concept (e.g., Alling 1918, 1920; Johnson 1917; Ogilvie 1902) alluded to morphological evidence, such as cirques and moraines, as evidence for small alpine glaciers in a few of the highest Adirondack headwater valleys, but Fairchild (1913, 1932) considered a late Pleistocene phase of alpine glaciation to be unlikely. Craft (1969, 1976, 1979) concluded that landforms and sediments in multiple Adirondack valleys were the products of small alpine glaciers and suggested that some of the alpine glaciers may have extended down valley for several to more than 10 kilometers (km). However, more recent work on proglacial lake successions in the AuSable and Boquet valleys (Deimer and Franzi 1988; Franzi 1992; Franzi, Barclay, Kranitz, and Gilson 2015; Franzi et al. 2007; Rayburn et al. 2007) places significant constraints on the extent of possible former Adirondack alpine glaciation. Based on all the available evidence, we consider it unlikely that independent local glaciers fed by snowfall in the High Peaks region developed during the most recent deglaciation. Rather, the headwater valleys of the Adirondack High Peaks region were ice-free or occupied by remnant blocks of continental ice or ice-marginal lakes as the LIS wasted and receded from the region.

PALEOGEOGRAPHIC RECONSTRUCTIONS Reconstructing the paleogeography of the Adirondack and adjoining regions depends upon stratigraphic analysis of glacial, lacustrine, and marine deposits and upon the spatial distributions of ice marginal and proglacial lake deposits and landforms. Deglacial reconstructions are often hampered by complex or ambiguous stratigraphic relationships, poor preservation or lack of exposure of physical evidence, and outdated or unavailable stratigraphic documentation over large areas. Consequently, paleogeographic reconstructions must extend from areas where the stratigraphy is well documented into adjacent areas, which often have little or no stratigraphic control. The paucity of detailed contemporary glacial-stratigraphic information is particularly acute throughout most of the Adirondack Uplands, although the works of Craft (1969, 1976, 1979), Gurrieri and Musiker (1990), Muller, Sirkin, and Craft (1993) are notable exceptions. The paleogeographic reconstructions presented here are derived from detailed field studies of glacial foreland deposits and landforms in the western Mohawk Valley (e.g., Muller, Franzi, and Ridge 1986; Ridge 1997; Ridge and Franzi 1992; Ridge et al. 1991), the Ontario and St.

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Lawrence lowlands (e.g., Muller and Prest 1985; Occhietti, Parent, Shilts, Dionne, Govare, and Harmard 2001; Pair, Karrow, and Clark 1988; Pair and Rodrigues 1993; Richard and Occhietti 2005), the Champlain Lowland (Chapman, 1937; Cronin et al. 2012; Denny 1974; Franzi et al. 2007; Parent and Occhietti 1988; Rayburn et al. 2011, 2007, 2005) and the upper Hudson drainage basin (Connally and Sirkin 1973, 1971; DeSimone et al. 2008; DeSimone and LaFleur 2008; Dineen and Hanson 1992; Stanford 2009). Extrapolation of ice margins from these areas into the Adirondack Uplands was guided by the use of glacier-profile models (Benn and Hulton 2010; Schilling and Hollin 1981) along well-constrained ice flow lines and the projection of ice-surface equipotential lines into regions with less stratigraphic control. Franzi (2002, unpublished) and (Franzi et al. 2015) used this technique to correlate ice margin positions in the AuSable, Boquet, and Saranac valleys of the northeastern Adirondack Upland. In most instances, these techniques produced realistic correlations but were most effective when used in combination with field evidence to correlate well developed ice-marginal deposits and landforms in adjacent valleys. Shorelines for the regional proglacial lakes Albany, Coveville, Fort Ann, and Iroquois, as well as the upper marine limit of the Champlain Sea were recreated by fitting a trend surface to the surface elevations of shoreline deposits (compiled by Rayburn 2004 and DeSimone 2016, personal communication) and intersecting the lake planes with a 50 m digital elevation model (DEM) for New York and adjacent parts of New England and southeastern Canada. Smaller Adirondack proglacial lake shorelines were approximated by projecting a first-order trend surface from their presumed lake outlet elevation at a northward gradient of 0.75 m/km (Denny 1974; Franzi 1992; Franzi et al. 2015; Rayburn et al. 2005). Numerical ages for the ice front positions across central and eastern New York that appear on Figure 2 were transferred to New York from New England as follows. A precise chronology of deglaciation was developed in New England based on a calibrated 5659-year varve chronology, varve counts, and radiocarbon ages tied to the varves (Ridge et al. 2012), as well as cosmogenic 10Be ages of glacial boulders (Balco, Briner, Finkel, Rayburn, Ridge, and Schaefer 2009). Correlations between ice margins and events in New England and New York, and thus the transfer of numerical ages to New York, are based on the correlation of paleomagnetic records of remanent declination in fine-grained, laminated glaciolacustrine deposits in both areas (Ridge 2003, 2004; Ridge et al. 1990). It should be emphasized that this correlation has a greater uncertainty than just the uncertainty of radiocarbon ages or their calibration. Paleomagnetic declination values have an uncertainty of up to +4ยบ and declination records have a time lag of up to 2-3 centuries between the two areas dependent on the rate of westward drift of dipole and non-dipole components of the geomagnetic field through time. In other words, like today, the two areas rarely have exactly the same geomagnetic declination at the same time, but are generally within 4-5ยบ. Ages for ice margin positions in both New England and New York are constantly revised as new radiocarbon ages, improved radiocarbon calibration, improved calibration of the varve chronology in New England, and new paleomagnetic data become available (cf. Ridge 2016, for the most

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recent update). All radiocarbon dates in this manuscript are calibrated using Calib 7.0.4 and the IntCal13 data set (Reimer et al. 2013; Stuiver and Reimer 1993), and they are presented at 2Ď&#x192; uncertainty. Calibrated ages alleviate radiocarbon age variability due to temporal variations in 14C production rates, reservoir effects, variable isotopic fractionation, and contamination. The reader is referred to Reimer et al. (2013) or Stuiver and Reimer (1993) for further explanation of radiocarbon calibration methods. Figure 2: Deglacial chronology for New York showing the locations of principal moraines and other ice marginal deposits and landforms (modified after Ridge 2003, 2016). Numbers indicate ages in calibrated (U-TH) kyr. B.P. Arrows indicate ice-front positions that are the limits of glacial readvances.

REGIONAL SYNTHESIS

Early Deglaciation from the Last Glacial Maximum (LGM) The LIS reached its last glacial maximum (LGM) position in southern New York between 28-23 cal. kyr B.P. (Ridge 2003, 2004, 2016) (Figure 2). The Adirondack region probably influenced subglacial ice flow, but it is likely that ice was actively flowing over the highest peaks (Ogilvie 1902; Taylor 1897) at the LGM, although, as on high peaks in New England,

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it may not have significantly eroded high elevation land surfaces (Bierman, Davis, Corbett, Lifton, and Finkel 2015). Deglacial drawdown of the LIS into major lowlands caused thinning of ice over upland regions and lobation of the ice front. Proglacial Lake Albany (LaFleur 1968; Woodworth 1905a) fronted the receding ice margin in the Hudson Lowland during the initial stages of deglaciation and expanded northward with ice recession. The general northward recession was punctuated by sometimes extensive but short-lived readvances in the Hudson and Mohawk lowlands. The southwestern Adirondacks probably first emerged from the ice about 18-19 cal. kyr B.P. and divergence into separate ice streams began at this time (Ridge et al. 1991). Ice flow into the Mohawk Valley eventually diverged into eastern (Mohawk) and western (Oneida) ice lobes as ice thinning and recession continued. Proglacial lakes at the ice margins and between the opposing Mohawk and Oneida ice lobes eventually gave way to the first period of free eastward drainage and fluvial conditions (Figure 3) as the ice margin evacuated the eastern end of the Mohawk Valley. This fluvial interval is represented by an erosional unconformity and fluvial gravel in western Mohawk Valley stratigraphic sequences (Muller et al. 1986; Ridge 1997; Ridge et al. 1991) that correlate with the Erie Interstadial (Mรถrner and Dreimanis 1973) or Erie Phase (Karrow, Dreimanis, and Barnett 2000) in eastern Great Lakes stratigraphic nomenclature. The fluvial gravel and unconformity were later buried by deposits of glacial readvances and lakes during the Valley Heads glaciation as discussed below. Figure 3: Time-distance diagram showing the lithologic relationships of late Wisconsinan stratigraphic units in the western Mohawk Valley (after Muller et al. 1986).

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Valley Heads Readvance and the St. Johnsville-Canajoharie Ice Margin In central New York, glacial ice from the Ontario Lowland pushed southward into the Finger Lakes region and reached its maximum extent in central New York at the outer Valley Heads Moraine. The Valley Heads Readvance marked the end of the Erie Interstadial and eastward fluvial drainage through the Mohawk Valley ceased. Drainage from the glacier and runoff from the unglaciated uplands at the Valley Heads maximum was diverted southward to the Susquehanna drainage basin (Figure 4). The Valley Heads moraines that formed along the Appalachian escarpment from the Finger Lakes region eastward to about Oneida consist of thick heads of outwash and ice-contact stratified drift in the valleys. These deposits form the present-day drainage divide between the Susquehanna and St. Lawrence drainage basins (Cadwell and Muller 2004). Figure 4: Paleogeography of glacial ice lobes and proglacial lakes in northeastern New York at the maximum extent of the Valley Heads Readvance in central New York. The abbreviation LM refers to proglacial Lake Miller in the upper West Canada Creek Valley. The brown triangles indicate the possible locations of nunataks as determined by glacier-profile modeling.

The Valley Heads readvance in the Finger Lakes region generally correlates with asynchronous readvances of the Mohawk and Oneida lobes in the western Mohawk Valley (Muller et al. 1986; Ridge 2003, 2004; Ridge, Brennan, and Muller 1990; Ridge and Franzi 1992). The Mohawk lobe advanced westward as the Salisbury Readvance (SA on Figure 2), fed by ice streaming through Sacandaga trough in the southeastern Adirondacks. Proglacial

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lakes were re-established in the western Mohawk Valley, and these lakes deepened and widened progressively as lower eastern outlets were blocked by the westward advancing Mohawk Lobe. The highest proglacial lake level, Lake Cedarville, drained southward through Cedarville col to the Unadilla River in the Susquehanna drainage basin (Ridge 1985; Ridge and Franzi 1992; Ridge et al. 1991). The Mohawk lobe receded from its Salisbury Readvance maximum as ice from the Oneida lobe continued its eastward advance into the Mohawk Valley as the Hinckley-St. Johnsville Readvance (Figure 4; SH on Figure 2; Ridge and Franzi 1992). Early recession of the Mohawk lobe may have been triggered by increased calving caused by rising lake water in the western Mohawk Valley, while the Mohawk Lobe advanced westward into a widening valley. Advancing Oneida lobe ice experienced the same lake level rise but instead was advancing eastward into a narrowing valley that diminished calving potential and appears to have stabilized the advance of the lobe. Oneida ice overrode varved lacustrine deposits that were deposited over older till deposits of Mohawk provenance (Hawthorne till of Figure 3), indicating that a short period of lacustrine sedimentation intervened between the Mohawk and Oneida advances (Ridge 1985; Ridge et al. 1990; Ridge and Franzi 1992). Proglacial Lake Cedarville may have fronted the advancing Mohawk and Oneida lobes during the Salisbury and Hinckley-St. Johnsville advances in the Mohawk Valley, but this lake lasted only until the Mohawk lobe receded far enough east to open drainage to Lake Schoharie. The Hinckley-St. Johnsville (SH on Figure 2; Oneida Lobe) and Canajoharie (Mohawk Lobe) ice margins shown on Figure 4 depict the deglacial paleogeography of northern New York at the culmination of the Valley Heads Readvance. Proglacial lakes Miller and Schoharie (Figure 4) were impounded along the margins of the Oneida and Mohawk lobes. Outflow from Lake Schoharie was directed southeastward through Catskill Creek to proglacial Lake Albany, which in turn drained southward through the Hellâ&#x20AC;&#x2122;s Gate threshold in New York City (Stanford 2009). Nunataks began to emerge as the ice thinned over the Adirondack High Peaks and the south-central highland regions. The suture between glacial ice sourced in the Ontario lobe and that sourced in the Hudson-Champlain lobe probably occurs in the highland formed by Snowy Mountain, Blue Mountain, and the High Peaks (Figure 4). The ice margin retreated briefly from its Valley Heads maximum before a short readvance to the Barneveld-Little Falls ice margin in the western Mohawk valley (BL on Figure 2; Ridge and Franzi 1992). This readvance was fronted by a lower level of Lake Schoharie (Delanson outlet; Lake Gravesville of Ridge and Franzi [1992]) in the Mohawk Valley. Lower Lake Schoharie drained to the Lake Amsterdam level, and eventually Lake Albany inundated the lower Mohawk Valley as ice recession uncovered the eastern end of the Mohawk Valley.

Ninemile Ice Margin The Ninemile ice margin depicts the deglacial paleogeography at the terminus of the Ninemile Readvance (Ridge and Franzi 1992) near Rome in the western Mohawk Valley (Figure 5). Deposits and landforms associated with the Stanwix Readvance (Fullerton 1971, 1980) may have been formed by the more extensive Ninemile Readvance (Ridge and

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Franzi 1992). Regional ice margin correlations suggested that the Ninemile Readvance may have been associated with the Luzerne Readvance in the upper Hudson Valley (Figure 2; Ridge 2003, 2004, 2016). Our placement of the Hudsonâ&#x20AC;&#x201C;Champlain ice margin north of the Luzerne Readvance position, however, is consistent with the asynchroneity of glacial readvances observed in the Mohawk Valley (Ridge 1985; Ridge et al. 1990; Ridge and Franzi 1992). Furthermore, DeSimone et al. (2008) and DeSimone and LaFleur (2008) questioned the physical evidence for the Luzerne Readvance and suggested that the ice marginal deposits and landforms described by (Connally and Sirkin 1971, 1973) represent a short-lived recessional moraine. The upper Hudson Valley ice margin depicted in Figure 5 lies approximately 10 km north of Fort Ann, near the point at which proglacial Lake Albany (ABII) drained to the Quaker Springs level (DeSimone et al. 2008). Figure 5: Paleogeography of glacial ice lobes and proglacial lakes in northeastern New York at the maximum extent of the Ninemile Readvance in the western Mohawk Valley. The abbreviations refer to proglacial lake Frenchville (LF) in the upper Mohawk Valley, proglacial Lake Port Leyden (Fairchild 1912) in the Black River Valley, and the Crescent (cc) and Ballston-Drummond (bd) distributary channels of the Iro-Mohawk River near Cohoes. The brown triangles indicate the possible locations of nunataks as determined by glacier-profile modeling.

Ridge and Franzi (1992) suggested that Lake Amsterdam occupied the western Mohawk Valley at the culmination of the Ninemile Readvance. Mohawk Valley lakes may also have been responsible for an early high phase of Lake Iroquois (Lake proto- or hyper-Iroquos; Domack, Leventer, Kopp, Lucas, Patacca and Scholz 2016; Domack, Scholz, Owen, Lothrop and Winsor 2016; Fairchild 1909; Fullerton 1971, 1980) in the eastern Oneida Lowland

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following recession of the Oneida Lobe from its Ninemile terminus. Base level controls for Mohawk Valley lakes at this time are problematic because the ice margin in the upper Hudson Valley was located well north of the confluence of the Mohawk and Hudson rivers, and the Hudson or Mohawk ice lobes could not have served as ice dams. The most likely controls for Lake proto- or hyper-Iroquois are bedrock constrictions in the Mohawk Valley at Moss Island in Little Falls or “The Noses” at Canajoharie. However, projection of the proto- or hyper-Iroquois lake terraces identified by Domack et al. (2016a, 2016b) fall close to the elevation of the Little Falls threshold but well below that of the Canajoharie threshold. These data are consistent with the Little Falls threshold as the outlet for Lake proto- or hyper-Iroquois but requires incision of the Canajoharie threshold prior to the creation of the lake. Late lake phases in the Mohawk Valley and Oneida Lowland probably predate the eastward drainage of proglacial lake outflow from the Great Lakes basins through the Mohawk Valley and may correlate with a brief period of westward ice marginal drainage in the Erie and western Ontario basins. The additional outflow from the proglacial Great Lakes established the Iro-Mohawk River in the Mohawk Valley (Figures (Figures 3 and 6), which may have incised the bedrock threshold at Little Falls and caused the drop of lake level from Lake proto- or hyper-Iroquois to Lake Iroquois (main phase) in the Oneida and Ontario lowlands. This outflow may also have facilitated the drop in lake level from Lake Albany II to Lake Quaker Springs in the Hudson Lowland. Wall (1995) estimated the maximum discharge of the Iro-Mohawk River exceeded 42,500 m3/s, which is more than ten times the maximum discharge of the modern Mohawk River over the past 90 years of record (DeSimone et al. 2008; Wall 2010). Ongoing work in the eastern Oneida Lowland (Domack et al. 2016a, 2016b) may shed light on the later stages of ice recession in the Mohawk Valley and Oneida Lowland. Lake Albany drained through a succession of short-lived lower lake phases (lakes Albany II, Quaker Springs, and Coveville [DeSimone et al. 2008]) as the Hudson–Champlain Lobe receded into the upper Hudson Valley. Proglacial lake level fell to the Lake Coveville level (Coveville Stage of Lake Vermont) when the ice margin receded to a position marked by the Street Road ice-contact delta north of Ticonderoga (DeSimone et al. 2008; Stanford 2009). The outlet location for Lake Coveville has not yet been established, but recent work in the upper Hudson Valley suggests that a sediment dam near the village of Halfmoon is a likely candidate (Figure 6; DeSimone et al. 2008). Eastward fluvial drainage from the Mohawk Valley initially entered proglacial Lake Albany II in two distributary channels; the Ballston and Crescent channels (Figure 5). The Ballston channel expanded northward and split into two separate channels, the Saratoga Lake and Round Lake channels, when proglacial Lake Albany II fell to Lake Quaker Springs and then to Lake Coveville level.

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Figure 6: Paleogeography of glacial ice lobes and proglacial lakes in northeastern New York at the Carthageâ&#x20AC;&#x201C;Loon Lakeâ&#x20AC;&#x201C;Elizabethtown ice margin. The abbreviation SIB refers to the Saranac Intramontane Basin (Buddington 1953). PProglacial lakes Chapel (LC) and Elizabethtown (LE) formed in front of the ice margin in the Keene and Boquet valleys, respectively (Franzi et al. 2016). Proglacial Lake Glenfield (LG) was impounded in the Black River Valley (Fairchild 1912). Ballston-Drummond (dc), Fish Creek (fc), and Anthony Kill (ak) distributaries of the Iro-Mohawk River drain into Lake Coveville in the Hudson and Champlain lowlands. The red circle indicates the location of the Elizabethtown musk-ox fossil in proglacial Lake Hoisington (Franzi et al. 2016).

Figure 7: Paleogeography of glacial ice lobes and proglacial lakes in northeastern New York at the maximum extents of proglacial lakes Iroquois in the Ontario and St. Lawrence lowlands and Coveville in the Champlain Lowland. The Crescent (cc) distributary channel of the Iro-Mohawk River remains active but the Ballston-Drummond (dc), Fish Creek (fc), and Anthony Kill (ak) are abandoned at this time.

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The three-channel distributary system (Stoller 1918) reached its full development in Lake Coveville (DeSimone et al. 2008). Flow in the Crescent channel occurred under steeper hydraulic gradients and progressively captured a greater proportion of fluvial throughflow from the Mohawk Valley. Eventually, all of the Iro-Mohawk River discharge was diverted to the Crescent channel (Figure 6). Fluvial drainage was established in the lower Hudson Valley south of the Halfmoon threshold and flowed southward to the Hudson estuary near New York City (Stanford 2009). The potholes at Cohoes were either exhumed or created after the onset of fluvial conditions in the lower Mohawk Valley. Some of the potholes described by James Hall (1871) were remarkably narrow (~1 m) and deep (>7 m) and may have formed by cavitation under extraordinarily high-magnitude flow conditions (Wall 2010). Cohoes Falls retreated rapidly from the vicinity of the present Hudson-Mohawk confluence and Iro-Mohawk River flow eroded the gorge below the falls. One of the potholes would later become the resting place for the Cohoes mastodon, but that fossil could not have been preserved as long as the Iro-Mohawk River remained active. The mastodon fossil yielded an age of 12.82-13.10 cal. kyr. B.P. (pooled mean NYSM VP101; Feranec and Kozlowski 2016), which post-dates the Iroquois breakout at Covey Hill, the drainage of Lake Iroquois to the Lake Frontenac level, and the abandonment of the Iro-Mohawk River (Figures 6, 7, and 8). Proglacial lakes formed in the north-draining Finger Lakes valleys as ice receded from the Valley Heads Moraine (Figure 5; Cadwell and Muller 2004; Mullins and Hinchey 1989; Mullins et al. 1996) in central New York. Initially, the lakes drained south across the moraine, but as ice recession continued, the lakes expanded, lower outlets were uncovered, and later outflow, supplemented by outflow from proglacial lakes in the Great Lakes region, was diverted eastward along the ice front. The eastward ice-marginal drainage carved an extensive system of ice marginal channels across interfluves along the northern flank of the Appalachian Plateau. The channel system is best preserved between Syracuse and Oneida where there is evidence for at least two episodes of channel cutting by ice marginal, supraglacial, or subglacial drainage (Sissons 1960). Most of the south-central Adirondack highlands and the southern High Peaks regions were probably ice-free and several High Peaks nunataks remained at this time (Figure 5). The ice margin generally followed the southwest-northeast trend of the low mountains that form the southern flank of the Saranac Intramontane Basin west of the High Peaks region. Meltwater was directed southwestward to proglacial lakes in the Black River Valley and ultimately to the western Mohawk Valley. Meltwater east of the High Peaks region flowed southward via the Hudson and Schroon rivers to the upper Hudson Lowland near Glens Falls (Figure 5).

Carthage–Loon Lake–Elizabethtown Ice Margin Lake Coveville expanded northward as the ice margin receded into the Champlain Lowland and small proglacial lakes formed in north-draining tributaries in the northeastern Adirondack Mountains. The Carthage–Loon Lake–Elizabethtown ice margin (CLLE; Figure 6) is marked by ice-contact deltaic deposits and ice-marginal channels in the AuSable,

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Boquet, and Black valleys, but it is not associated with any known readvances. The ice margin is significant, because its age is constrained by a radiocarbon age on a musk-ox vertebrae of 11.28 ± 0.11 14C kyr. BP (AA-4935; Cadwell and Pair 1991), which corresponds to a calibrated age between 13.03–13.45 cal. kyr. B.P. when corrected for estimated δ13C (Rayburn et al. 2007, 2011). The musk-ox bone was discovered by a gravel pit operator in prodeltaic facies in a small ice-contact delta near Elizabethtown. The CLLE ice margin correlates with the Loon Lake stand of Denny (Denny 1974) in the upper Saranac River basin and the Elizabethtown ice margin (Franzi et al. 2015; Rayburn et al. 2007) in the AuSable, Boquet and Champlain valleys (Figure 6). Proglacial lake outflow in the AuSable, Boquet, and Black valleys was eastward to Lake Coveville in the Champlain Valley. The ice margin generally follows the northern flank of the SIB westward to the northern end of the Black River Valley. Large masses of stagnant ice were left in the SIB and thick deposits of ice-contact stratified drift and outwash were deposited by meltwater streams that drained westward from the upper Saranac River basin to the upper St. Regis River basin (Denny 1974). The meltwater outflow eventually entered proglacial lakes in the lower Black River Valley and ultimately into proglacial Lake Iroquois, which occupied the Ontario Lowland (Figure 6). Lake Iroquois received inflow from proglacial lakes in the eastern Great Lakes basins (Muller and Prest 1985) and discharged eastward across the Little Falls threshold via the Iro-Mohawk River. It is probable that all of the Iro-Mohawk River discharge flowed through the southernmost, or Crescent, distributary channel at Cohoes (Figure 6).

Ellenburg–Plattsburgh Ice Margin Lakes Iroquois and Coveville expanded northward with further ice recession in the St. Lawrence and Champlain lowlands, respectively. The Ellenburg–Plattsburgh ice margin (Franzi et al. 2015) corresponds to Denny’s ice front position 8 (Denny 1974) and depicts proglacial Lake Iroquois in the Ontario and St. Lawrence valleys and Lake Coveville in the Champlain Valley near their maximum extents (Figure 7). The ice margin follows the trend of a small east-west trending recessional moraine north of Clinton Mills and the Ellenburg Moraine, a large generally north-south trending moraine that crosses the upper North Branch of the Chazy River Valley near Ellenburg Depot (Denny 1974; Franzi et al. 2007). A small proglacial lake impounded in front of the Ellenburg Moraine in the upper North Branch valley probably drained southeastward along the ice front (Franzi et al. 2007, 2015). The outflow may be responsible for ice marginal channels and ice-contact stratified deposits just north of Plattsburgh (Franzi et al. 2015). These deposits and landforms immediately predate the breakout of Lake Iroquois into the Champlain Lowland.

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Lake Iroquois Breakout and Lakes Frontenac and Fort Ann Ice recession from the Ellenburg-Plattsburgh ice margin uncovered the Covey Hill threshold, and Lake Iroquois drained catastrophically across the St. Lawrenceâ&#x20AC;&#x201C;Champlain divide into Lake Coveville (Denny 1974; Franzi et al. 2007; Franzi, Rayburn, Yansa, and Knuepfer 2002; Rayburn et al. 2005). The breakout released 570 Âą 85 km3 of water storage from the Ontario and St. Lawrence lowlands at an estimated discharge of 83,000-92,000 m3/s during the waning stages of the flood (Rayburn 2004; Rayburn et al. 2005). Proglacial lake level in the Ontario and St. Lawrence lowlands dropped by about 14 m, and the Lake Iroquois outlet near Rome was abandoned (Figures 7 and 8). The Iroquois breakout ended eastward Iro-Mohawk River drainage in the Mohawk Lowland and represents the earliest opportunity for the preservation of the Cohoes mastodon fossil in the pothole near Cohoes Falls (DeSimone et al. 2008; Wall 2010). Falling water level in the Ontario and St. Lawrence lowlands stabilized at the Covey Hill threshold and Lake Frontenac became established with outflow through The Gulf at Covey Hill (Muller and Prest 1985; Pair and Rodrigues 1993). Sustained outflow of approximately 56,000 m3/s (Rayburn et al. 2005) from Lake Frontenac carved The Gulf, a narrow, 1.5 km-long gorge cut deeply into the Potsdam Sandstone south of Covey Hill (Denny 1974; Muller and Prest 1985; Pair and Rodrigues 1993). Figure 8: Paleogeography of glacial ice lobes and proglacial lakes in northeastern New York showing proglacial Lake Frontenac in the St. Lawrence Lowland and proglacial Lake Coveville in the Champlain Lowland. The spatial extents of the Clinton County Flat Rocks was derived from Denny (1974).

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The flood waters were directed southeastward along the ice front in the Champlain Lowland, stripping the surficial cover from large areas and carving channels and plunge pools in the Potsdam Sandstone. The intense scour created a discontinuous 30 km long belt of exposed sandstone surfaces that are known locally as the Clinton County Flat Rocks (Figure 8; Denny 1974; Franzi et al. 2007; Rayburn et al. 2005; Woodworth 1905a, 1905b). The physical environment of the Flat Rocks today is characterized by extreme deficiencies in nutrients and soil moisture, and some locations host globally rare sandstone-pavement jack pine barrens (Franzi and Adams 1993). The ice-marginal flood waters deposited the coarse ice-contact boulder deposits that comprise Cobblestone Hill where they entered Lake Coveville at the southeastern margin of Altona Flat Rock (Woodworth 1905b; Denny 1974; Franzi et al. 2002; Rayburn et al. 2005). Franzi et al. (2002) traced Coveville shorelines northward to Cobblestone Hill and recognized that the deposits occur in two terraces that correspond roughly to Coveville and Fort Ann proglacial lake levels in the Champlain Lowland. They proposed that transmission of the Iroquois breakout floodwave through the Champlain and upper Hudson lowlands caused the failure of the Coveville threshold and caused Lake Coveville to drain to the Fort Ann level (Figure 8; Franzi et al. 2002; Rayburn et al. 2005). Falling water levels in the Champlain Lowland encountered higher, temporary outlet channels near the Fort Ann threshold, creating a succession of ephemeral Lake Fort Ann strandline features in the lowland (Rayburn 2004; Rayburn et al. 2005). The highest of these features define the “Upper Fort Ann” water surface but Lake Fort Ann only became stable at the “Lower Fort Ann” level as continued incision uncovered the bedrock threshold near Fort Ann (Chapman 1937; Rayburn 2004; Rayburn et al. 2005). The drainage of Lake Coveville to the upper Lake Fort Ann level released an additional 130 ± 20 km3 from water storage in the Champlain Lowland for a total storage loss of approximately 700 km3 for the combined Iroquois–Coveville breakouts. The lake outflow was directed southward into the upper Hudson Lowland, where erosion exhumed the pre-glacial Fort Ann Branch and BattenkillHudson channels used by the Hudson River today.

Drainage of Lake Frontenac Lake Frontenac drained as the ice front receded from the north flank of Covey Hill, and lake levels in the Ontario–St. Lawrence and Champlain lowlands merged at the Fort Ann level (Figure 9). The Iroquois and Frontenac drainage events are recorded by erosional unconformities and coarse flood deposits in cores and outcrops in the northern Champlain Lowland. Franzi et al. (2007) estimated the duration of Lake Frontenac to be about 50 years based upon estimates from compositional changes in varved clay deposits at Whallonsburg in the Champlain Lowland. Unlike the earlier Lake Iroquois breakout, the drainage of Lake Frontenac left little physical evidence of a catastrophic discharge event. That evidence may be buried by younger deposits or the drainage may have occurred as a broad flow over, under, or through the ice front (Rayburn et al. 2005; Franzi et al. 2007). The drainage of Lake Frontenac released about 2,500 ± 375 km3 (Rayburn 2004; Rayburn et al. 2005) of storage in the Ontario and St. Lawrence lowlands that was directed southward into the upper Hudson lowland. Lake Fort Ann existed for about 170 years,

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as evidenced by post-Lake Coveville varved clays from sediment cores collected from the Champlain Lowland (Rayburn et al. 2011). Figure 9: Paleogeography of glacial ice lobes and proglacial lakes in northeastern New York following the drainage of Lake Frontenac and the expansion of Lake Fort Ann into the St. Lawrence Lowland. The spatial extents of the Clinton County Flat Rocks was derived from Denny (1974). The brown triangle marks the location of Covey Hill.

Champlain Sea Ice-margin recession in the lower St. Lawrence Lowland near Warrick, Quebec opened a connection to the Atlantic Ocean causing Lake Fort Ann to drain, releasing approximately 1,500 km3 of proglacial lake water to the Gulf of St. Lawrence (Rayburn et al. 2005), and marine water inundated the isostatically depressed St. Lawrence and Champlain lowlands (Figure 10). The marine episode, known as the Champlain Sea, is marked by abundant marine microfauna, invertebrates, fish, and mammals in stratigraphic sections in the Champlain and St. Lawrence lowlands (Cronin 1988; Cronin et al. 2012; Feranec, Franzi, and Kozlowski 2014; Harrington 1988; Hunt and Rathburn 1988; Steadman, Kirchgasser, and Pelky, 1991). Notable marine mammal fossils from Champlain Sea deposits in New York include the Norfolk whale (Steadman et al. 1991) from the St. Lawrence Lowland near Potsdam and two seal fossils from Plattsburgh (Feranec et al. 2014) in the Champlain Lowland. The marine incursion began between 13.12 and 12.85 cal. kyr. B.P. (Cronin et al. 2008, 2012), but the transition was not straightforward. Micropaleontological and isotopic evidence from cores of proglacial lake and marine deposits in the St. Lawrence and Champlain Valleys (Rayburn et al. 2007, 2011; Cronin et al. 2008, 2012) indicate that VOLUME 21

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freshwater conditions returned shortly after the initial marine incursion before reverting to the main marine phase of the Champlain Sea. Cronin et al. (2012) attributed the freshening event to influx of large quantities of freshwater from proglacial Lake Agassiz in west-central Canada. Rayburn et al. (2011) estimated the duration of the freshening interval to be about 120 years. The freshwater interval that was followed by a mixed â&#x20AC;&#x153;transitional phase,â&#x20AC;? containing both freshwater ostracodes and marine forams following the freshening event, likely marked punctuated shorter pulses of high-discharge freshwater influx during the return to full marine conditions. Marine conditions persisted until differential isostatic rebound raised the northern portion of the basin above sea level and Lake Champlain became established in the Champlain Lowland. The Champlain Sea-Lake Champlain transition began around 9.4 cal. kyr. B.P. and was completed by about 8.6 cal. kyr. B.P. (Belrose 2015). Figure 10: Paleogeography of glacial ice lobes and proglacial lakes in northeastern New York at the maximum extent of the Champlain Sea.

CONCLUDING REMARKS

Rate of Ice Recession Ice recession from the terminal moraine in New York began approximately 23 cal. kyr. B.P. in the lower Hudson Valley (Figures 2 and 11), and by 16-17 cal. kyr. B.P., the ice front reached the Albany region and Mohawk Valley. The average retreat rate in the lower Hudson Valley was approximately 0.03 km/yr, but this long-term average rate includes several possible short136

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term readvances. Long-term average post-Valley Heads retreat rates are nearly four times greater (about 0.14 km/yr; Figure 11) in the upper Hudson and Champlain lowlands. Franzi et al. (2007) reported short-term recession rates in the range of 0.19 to 0.44 km/yr in the Champlain Lowland. Recession rates of this magnitude are typical of calving ice margins that are associated with unstable buoyant ice (Benn, Warren, and Mottram 2007; Joughin, Smith, Shean, and Floricioiu 2014). We consider it likely that rapid post-Valley Heads recession rates in the Ontario-St. Lawrence and Champlain lowlands were a function of late-glacial climatic amelioration, changing patterns of ice flow and calving dynamics. The rate of ice retreat in the deep lake basins adjacent to the Adirondack Upland contrast sharply with that in the lower Hudson and Mohawk valleys, where ice recession was interrupted by short-term readvances. Figure 11: Comparison of ice recession rates in the lower Hudson and upper Hudson-Champlain lowlands. Abbreviations are keyed to Figure 2. The ice margin position at the time of the Champlain Sea incursion is approximated by the ice front position depicted in Figure 9, which most likely produces and under estimate of recession rate. The location of the Lake Albany II (ABII) ice margin is shown in Figure 5.

Paleoclimate Implications The weakening of Atlantic Meridional Overturning Circulation (AMOC) caused by decreasing North Atlantic salinity is often invoked to explain global climate change. Broecker et al. (1989) suggested that the diversion of Lake Agassiz outflow from the Gulf of Mexico to the North Atlantic via the Great Lakes and St. Lawrence Lowland may have triggered the late Pleistocene Younger Dyras climate reversal. This hypothesis has been

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the subject of considerable debate (cf. Cronin et al. 2012). Rayburn et al. (2005, 2007) noted the correspondence in age between steady-state outflow and breakout flood events from large proglacial lakes in the Ontario, St. Lawrence, and Champlain lowlands and the record of late glacial climate changes from the Greenland GISP2 (Taylor et al. 1993) ice core and deep-sea sediment cores (Hughen, Southon, Lehman, and Overpeck 2000; Figure 12). Furthermore, immediately following the initial establishment of the Champlain Sea, a strong freshwater discharge flowing through the St. Lawrence Lowland caused a return to freshwater conditions in the Champlain Sea basin for at least a century. The freshwater phase was followed by shorter pulses of high freshwater influx during the transition back to full-marine conditions (Cronin et al. 2012). Rayburn et al. (2011) dated the transition between 12.74-13.07 cal. kyr. B.P., which is supported by a varve-count estimate that the transition occurred at least 330 years following the establishment of Covey Hill ice margin. The radiocarbon age/varve correlation agrees well with the Elizabethtown ice margin age and places the cessation of large meltwater discharges at the inception of the Younger Dryas (Figure 12). The timing, magnitude and duration of late glacial freshwater discharges from the St. Lawrence and Champlain Valley region may have been sufficient to affect AMOC and trigger the Younger Dryas interval (Figure 12). Figure 12: Timing of proglacial lake phases and breakout events in the Champlain Lowland and the late Pleistoceneearly Holocene climate variability, as recorded by the yearly average electrical conductivity in the GISP2 ice core at Summit, Greenland (Taylor et al. 1993).

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ACKNOWLEDGEMENTS

The authors would like to thank the U.S. Geological Survey Global Change Program for funding our research in the Champlain and St. Lawrence lowlands. Work by J. Ridge was partly funded by a grant from the National Science Foundation (EAR award #0639830 in Sedimentary Geology and Paleobiology). John Rayburn received funding from a Geological Society of America Student Research Grant, a U.S. Department of Education Fellowship under the Graduate Assistantships in Areas of National Need program, and a United States Geological Survey Mendenhall Fellowship. We offer thanks to Dr. Thomas Stafford for the geochemical, amino acid, and radiometric work on the Elizabethtown musk-ox bone and Drs. David Stedman and Norton Miller, New York State Geological Survey, who provided paleontological details from the Elizabethtown site. Robert Feranec of the New York Geological Survey provided information on the Phocid seal bones discovered in Plattsburgh in 2009 (Feranec, Franzi, and Kozlowski 2014) and prepared the specimen for radiocarbon dating at NOSAMS with funds provided by the New York State Geological Survey. The National Oceanic and Atmospheric Administration provided bathymetric DEM data for lakes Ontario and Erie and Dr. Thomas Manley (Middlebury College) provided bathymetric data for Lake Champlain. The authors extend their thanks to Dr. Andrew Kozlowski of the New York State Geological Survey for his thoughtful review of the manuscript. L I T E R AT U R E C I T E D

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Gurrieri, J.T. and L.B. Musiker. 1990. “Late Wisconsinan ice margins and recessional events in the north-central Adirondack Mountains, New York,” Northeastern Geology, 12: 185-197. Hall, J.M. 1871. “Notes and observations of the Cohoes mastodon,” Cabinet of Natural History Report, 21: 98-148. The University of the State of New York. Harrington, C.R. 1988. “Marine mammals of the Champlain Sea, and the problem of whales in Michigan,” in N.R. Gadd (Ed.), Late Quaternary development of the Champlain Sea basin, 225-240. Geological Association of Canada. Hess, D. 2009. “Geospatial analysis of controls on subglacial bedform morphometry in the New York Drumlin field,” Earth Surface Processes and Landforms, 34: 1126-1135. Hughen, K.A., J.R. Southon, S.J. Lehman, and J.T. Overpeck. 2000. “Synchronous radiocarbon and climate shifts during the last deglaciation,” Science, 290: 1951-1954. Hunt, A.S. and A.E. Rathburn. 1988. “Microfaunal assemblages of the southern Champlain Sea piston cores,” in N. R. Gadd (Ed.), The late Quaternary development of the Champlain Sea basin, 145-154. Geological Association of Canada. Johnson, D.W. 1917. “Date of local glaciation in the White, Adirondack and Catskill mountains,” Geological Society of America Bulletin, 28: 543-552. Joughin, I., B.E. Smith, D.E. Shean, and D. Floricioiu. 2014. “Brief Communication: Further summer speedup of Jakobshavn Isbræ,” The Cryosphere, 8(1): 209-214. Kerr, M., and N. Eyles. 2007. “Origin of drumlins on the floor of Lake Ontario and in upper New York State,” Sedimentary Geology, 193(1-4): 7-20. LaFleur, R.G. 1968. “Glacial Lake Albany,” in R. W. Fairbridge (Ed.), The Encyclopedia of Geomorphology, 455-456. Reinhold Book Corporation. Muller, E.H., D.A. Franzi, and J.C. Ridge. 1986. “Pleistocene geology of the western Mohawk Valley, New York,” in D. H. Cadwell (Ed.), The Wisconsinan Stage of the First Geological District, eastern New York, 143-157. Muller, E.H. and V.K. Prest. 1985. “Glacial lakes in the Ontario basin,” in P.F. Karrow and P.E. Calkin (Eds.), Quaternary Evolution of the Great Lakes, Special Paper 30: 213-229. Geological Association of Canada. Muller, E.H., L. Sirkin, and J.L. Craft. 1993. “Stratigraphic Evidence of a Pre-Wisconsinan Interglaciation in the Adirondack Mountains,” Quaternary Research, 40: 163-168. Mullins, H.T. and E.J. Hinchey. 1989. “Erosion and infill of New York Finger Lakes: Implications for Laurentide ice sheet deglaciation,” Geology, 17: 622-625.

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Mullins, H.T., E.J. Hinchey, R.W. Wellner, D.B. Stephens, W.T. Anderson., T.R. Dwyer, et al. 1996. “Seismic stratigraphy of the Finger Lakes: A continental record of Heinrich event H-1 and Laurentide ice sheet instability,” in H.T. Mullins and N. Eyles (Eds.), Subsurface Geologic Investigations of New York Finger Lakes: Implications for Late Quaternary Deglaciation and Environmental Change, 1–35. Geological Society of America. Occhietti, S., M. Parent, W.W. Shilts, J. Dionne, E. Govare, and D. Harmard. 2001. “Late Wisconsinan glacial dynamics, deglaciation, and marine invasion in southern Quebec,” in T. K. Weddle and M. J. Retelle (Eds.), Deglacial history and relative sea-level changes, northern New England and adjacent Canada, 243-270. Geological Society of America. Ogilvie, I.H. 1902. “Glacial phenomena in the Adirondacks and Champlain Valley,” Journal of Geology, 10: 397-412. Pair, D.L., P.F. Karrow, and P.U. Clark. 1988. “History of the Champlain Sea in the central St. Lawrence Lowland, New York,” in N. R. Gadd (Ed.), Late Quaternary development of the Champlain Sea basin, 107-123. Geological Association of Canada. Pair, D.L. and Rodrigues, C.G. 1993. “Late Quaternary deglaciation of the southwestern,” Geological Society of America Bulletin, 105: 1151-1164. Parent, M. and S. Occhietti. 1988. “Late Wisconsinan deglaciation andChamplain Sea invasion in the St. Lawrence valley, Que´bec,” Géographie Physique et Quaternaire, 42: 215-246. Rayburn, J.A. 2004. Deglaciation of the Champlain Valley New York and Vermont and its possible effects on North Atlantic climate change. Ph.D. dissertation, Binghamton, NY: Binghamton University. Rayburn, J.A., T.M. Cronin, D.A. Franzi, P.L.K. Knuepfer, and D.A. Willard. 2011. “Timing and duration of North American glacial lake discharges and the Younger Dryas climate reversal,” Quaternary Research, 75(3): 541-551. Rayburn, J.A., D.A. Franzi, and P.L.K. Knuepfer. 2007. “Evidence from the Lake Champlain Valley for a later onset of the Champlain Sea and implications for late glacial meltwater routing to the North Atlantic,” Palaeogeography, Palaeoclimatology, Palaeoecology, 246(1): 62-74. Rayburn, J.A., P.L.K. Knuepfer, and D.A. Franzi. 2005. “A series of large, Late Wisconsinan meltwater floods through the Champlain and Hudson Valleys, New York State, USA,” Quaternary Science Reviews, 24: 2410-2419. Reimer, P.J., E. Bard, A. Bayliss, J.W. Beck, C. Bronk-Ramsey, C.E. Buck, et al. 2013. “IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0–50,000 Years cal BP,” Radiocarbon, 55: 1869-1887. Richard, P.J.H. and S. Occhietti, S. 2005. “14C chronology for ice retreat and inception of Champlain Sea in the St. Lawrence Lowlands, Canada,” Quaternary Research, 63(3): 353-358.

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Ridge, J.C. 1985. The Quaternary glacial and paleomagnetic record of the West Canada Creek and western Mohawk Valleys of central New York. Ph.D. dissertation, Syracuse, NY: Syracuse University. Ridge, J.C. 1997. “Shed Brook discontinuity and Little Falls gravel: evidence for Erie Interstade in central New York,” Geological Society of America Bulletin, 109: 652-665. Ridge, J.C. 2003. “The last deglaciation of the northeastern United States: a combined varve, paleomagnetic, and calibrated 14C chronology,” New York State Museum Bulletin, 497: 15-45. Ridge, J.C. 2004. “The Quaternary glaciation of western New England with correlations to surrounding areas,” in J. Ehlers and P.L. Gibbard (Eds.), Quaternary Glaciations - Extent and Chronology, Part II: North America, 202206. Elsevier B.V. Ridge, J.C. 2016. “The North American Glacial Varve Project.” Available at http://eos.tufts. edu/varves. Ridge, J.C., G. Balco, R.L. Bayless, C.C. Beck, L.B. Carter, J.L. Dean, et al. 2012. “The new North American Varve Chronology: A precise record of southeastern Laurentide Ice Sheet deglaciation and climate, 18.2-12.5 kyr BP, and correlations with Greenland ice core records,” American Journal of Science, 312: 685-722. Ridge, J.C., W.J. Brennan, and E.H. Muller. 1990. “The use of paleomagnetic declination to test correlations of late Wisconsinan glaciolacustrine sediments in central New York,” Geological Society of America Bulletin, 102: 26-44. Ridge, J.C. and D.A. Franzi. 1992. “Late Wisconsinan glacial lakes of the Western Mohawk Valley region of central New York,” in R.H. April (Ed.), Field Trip Guidebook, 970120. New York State Geological Association. Ridge, J.C., D.A. Franzi, and E.H. Muller. 1991. “Late Wisconsinan, pre-Valley Heads glaciation in the western Mohawk Valley, central New York, and its regional implications,” Geological Society of America Bulletin, 103(8): 1032-1048. Schilling, D.H. and J.T. Hollin. 1981. “Numerical reconstructions of valley glaciers and small ice caps,” in D.H. Denton and T.J. Hughes (Eds.), The last great ice sheets, 2070220. New York: John Wiley and Sons. Sissons, J.B. 1960. “Subglacial, marginal, and other glacial drainage in the Syracuse-Oneida area, New York,” Geological Society of America Bulletin, 71(11): 1575-1588. Stanford, S.D. 2009. “Onshore record of Hudson River drainage to the continental shelf from the late Miocene through the late Wisconsinan deglaciation, USA: synthesis and revision,” Boreas, 39(1): 1-17.

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Steadman, D.W., W.T. Kirchgasser, and D.M. Pelky. 1991. “A late Pleistocene white whale (Delphinapterus leucas) from Champlain Sea sediments in northern New York,” in E. Landing (Ed.), Studies in Stratigraphy and Paleontology in Honor of Donald W. Fisher, 339-345. The University of the State of New York. Stoller, J.H. 1918. “Geology of the Cohoes quadrangle,” New York State Museum Bulletin, 215-216. The University of the State of New York. Stuiver, M. and P.J. Reimer. 1993. “Extended 14C database and revised CALIB radiocarbon calibration program,” Radiocarbon, 35: 215-230. Taylor, B.F. 1897. “Lake Adirondack.” The American Geologist, 19: 392-396. Taylor, K.C., G.W. Lamorey, G.A. Doyle, R.B. Alley, P.M. Grootes, P.A. Mayewski, et al. 1993. “The ‘flickering switch’ of late Pleistocene climate change,” Nature, 361: 432-436. Wall, G.R. 1995. Postglacial drainage in the Mohawk River Valley with emphasis on paleodischarge and paleochannel development. Ph.D. dissertation, Troy, NY: Rensselaer Polytechnic Institute,. Wall, G.R. 2010. “A new look at the formation of Cohoes Falls on the Mohawk: 4.” Presented at the Mohawk Watershed Symposium, March 10, 2016, Union College, Schenectady, NY. Available at http://ny.water.usgs.gov/pubs/abs/abs10-cohoesfalls-grwall.pdf. Woodworth, J.B. 1905a. “Ancient water levels of the Champlain and Hudson Valleys,” New York State Museum Bulletin, 84. The University of the State of New York. Woodworth, J.B. 1905b. “Pleistocene geology of the Mooers Quadrangle,” New York State Museum Bulletin, 83. The University of the State of New York.

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SOILS AND SOIL ACIDIFICATION IN THE ADIRONDACK MOUNTAINS RICHARD APRIL, 1 DIANNE KELLER, 1 AND MICHELE HLUCHY 2

1. Department of Geology, Colgate University, Hamilton, NY 13346, 315.228.7212, rapril@colgate.edu or dkeller@colgate.edu 2. Department of Environmental Studies and Geology, Alfred University, Alfred, NY 14802, 607.871.2838, fhluchy@alfred.edu

KEYWORDS:

Adirondacks, Soils, Acid Rain, Mineralogy, Weathering, Watershed Liming

ABSTRACT Soils in the Adirondack Mountains are relatively young, having formed in sediments deposited from the last major glacial episode that ended in the Adirondacks about 12,000 years ago. Most of the region is covered by an acidic, sandy, low-fertility soil called a Spodosol. Over time, Spodosols develop distinct colorful horizons that can be clearly distinguished in soil pits and road cuts. Because Spodosols are naturally acidic and contain marginal concentrations of some elements necessary to sustain a healthy forested ecosystem, they are somewhat fragile and susceptible to chemical changes. A century’s worth of acid deposition (“acid rain”) has depleted these soils of some important nutrients and has mobilized aluminum, an element linked to fish mortality and forest decline. Acid rain has declined over the past several decades, and lakes, streams, and soils are beginning to recover. How long it will take is still unknown.

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INTRODUCTION

What is Soil? What is soil and how is it different from sediment or just plain dirt? Sediment is particulate matter composed of inorganic mineral grains derived from both the physical and chemical weathering of rock. Depending on the source, sediment may contain just a few minerals derived from a single rock type or a plethora of minerals, some abundant and some minor, originating from different rock types present in the source area. Dirt is what you sweep from your porch when spring finally arrives or what collects in the crevices of your wood floors or in the corners of your attic. Soil, on the other hand, is an incredibly complex mixture of minerals, liquids, and gases, decomposed organic matter, and microbes. Some have called soil the “skin of the earth,” (Logan 1995) others “the biologically excited layer of earth’s crust” (Richter and Markewitz 1995). Either way it is a precious commodity, too often taken for granted. Soil can take decades to thousands of years to develop and evolve. It is a major component of our planet’s terrestrial ecosystem. Without soil there would be no terrestrial ecosystem.

SOIL IN THE ADIRONDACKS

Adirondack Glacial Sediments – the Precursor of Adirondack Soil Soils in the Adirondacks are less than 12,000 years old. Any regolith that was present before the last ice age was virtually stripped clean by the erosive action of the Wisconsinan glaciation. Soils in the southern U.S., on the other hand, where no recent glacial event reached, are hundreds of thousands, perhaps millions of years old. The parent material from which soil in the Adirondacks formed is the sediment deposited by the glacier after the great ice sheet melted away (see Franzi, this issue). We can determine what the nature of this parent material is by examining drill cores, sampling exposed sediments from road cuts and sand and gravel quarries, and by excavating soil pits to a depth of a meter or more to where the sediment has remained virtually unaltered by pedogenic processes. The minerals that compose these sediments vary from place to place depending on the composition of the local bedrock. But, in general, the most abundant minerals are quartz (SiO2), potassium feldspar (KAlSi3O8), and plagioclase feldspar (NaAlSi3O8 – CaAl2Si2O8) (Table 1). This is not surprising given that granitic bedrock occurs widely in the Adirondacks and is composed mainly of these minerals (see Chiarenzelli and Selleck, this issue). In locations where other types of bedrock dominate, such as metasedimentary rocks, anorthosites, gabbros, and amphibolites, the relative abundance of quartz and the feldspars, as well as amounts of accessory minerals (i.e., those present in the soil in concentrations of only a few percent or less) such as hornblende, garnet, ilmenite, magnetite, and pyroxene, will vary (April and Newton 1983; Newton et al. 1987). Soils initially inherit these same minerals from the sediment in which they form. But, as pedogenesis proceeds, weathering processes modify the mineral suite in soil by creating new ones and eliminating others.

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Table 1: Mineral abundances in the C-horizon determined by point counting of 300 grains (average of 81 samples; total of 100.1 due to rounding; one standard deviation in parentheses) (April et al. 1983). AVG. VOLUME %

STD. DEV

Quartz

39.0 (4.3)

K-feldspar

30.3 (1.9)

Plagioclase

17.8 (2.6)

Hornblende

3.5 (2.2)

Opaques

4.2 (1.1)

Pyroxene

0.7 (0.4)

Epidote

0.8 (0.4)

Garnet

0.6 (0.2)

Others

3.2 (0.6)

Total

100.1

THE BEGINNINGS OF ADIRONDACK SOIL Life does not take long to establish itself, even in such an inhospitable and barren terrain as the post-glacial Adirondacks. Primitive alpine plants, such as mosses, and composite organisms, such as lichens, took hold on the sand and bare rock left by the retreating glacier. Their presence began the process of turning sediment into soil by assimilating and recycling nutrients, retaining moisture, releasing organic acids, and, upon death, providing organic matter to the substrate. As temperatures warmed and the climate moderated, larger and more complex plants, such as shrubs, grasses, forbs, and trees began to thrive. Macroinvertebrates such as snails, millipedes, and spiders (McCay et al. 2013) joined the soil ecosystem, which was now also filled with microbes, and all of these organisms provided new means to decompose organic matter, aerate the soil, and construct channels for water to percolate. Soon boreal forests of spruce and fir covered the lowlands, spreading north and to higher altitudes as the climate moderated further. Finally, mixed conifer and hardwood forests comprising pine, hemlock, spruce, birch, ash, beech, and maple, to name just a few, covered much of the low- to middle-elevation slopes, with black spruce and tamarack occupying the wetland areas. It is important to note that as vegetation literally took root and organisms moved into new and available habitats in what was once the bare and lifeless glacial sediment, little by little an amazing transformation had begun â&#x20AC;&#x201D;the development of soil.

The Soil Profile â&#x20AC;&#x201D;Spodosols As you take a spade and drive it deep into a well-drained Adirondack forest soil, the cutting edge of the shovel will first penetrate a layer of fine roots and decomposed vegetation anywhere from a few centimeters (cm) to 25 cm thick. The vegetation is composed mainly of leaf and

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needle litter in various states of decay, with the remains of leaves and needles from the previous autumn senescence still visible on the surface grading to humus below. Some mineral matter will be present in this layer, likely mixed in by frost heave, tree throw, or invertebrate burrowing activity, but not much. This is the “O” or organic horizon of what will likely be a Spodosol (Figure 1), one of the twelve soil orders recognized in the U.S. Department of Agriculture’s soil taxonomy system and the most common soil type in the Adirondacks (Figure 2). A Spodosol is an acid soil, usually sandy and of low fertility, and characterized by a subsurface accumulation of organic matter, clay, and aluminum and iron oxides. It is typically found in regions of the world that experience a cold and wet temperate climate, and it represents little more than 4% of all soil orders mapped on our planet (NRCS 1999). The term Spodosol derives from the Greek “spodos,” which means wood ash, the characteristic color of the next horizon your spade will penetrate. This is the E-horizon, an ash-gray eluvial layer, the color of which is caused when iron and aluminum are leached out of this layer by the constant rain of organic acids produced by the decomposition of organic matter in the O-horizon above. The E-horizon is usually sandy, wavy, sometimes discontinuous, and consists mostly of resistant, uncoated quartz grains and little else. In the Adirondacks, however, clay minerals are also found here as they form from the intense weathering of silicate minerals that were once present in this horizon (April et al. 1986a). Figure 1: A typical Spodosol profile in the Adirondacks showing distinctive and colorful horizons. Depth from top O-horizon to bottom C-horizon (parent glacial sediment) is approximately 90 cm.

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Figure 2: Map of soil orders in and around the Adirondack Mountains. (Modified from the USDA Natural Resources Conservation Service [NRCS] World Soils Dataset).

Dig deeper and you encounter the B-horizon, or zone of accumulation. Here, the soil takes on a darker color and then eventually turns a bright orange-red, which then fades with depth. The dark layer just below the E-horizon is a zone where some organic matter (humic material), iron and aluminum sesquioxides, and fine clays washed down from above and accumulated. This top layer of the B-horizon (the Bs- [spodic] horizon, also sometimes referred to as the Bh- [humic] horizon), is not much thicker than 5-10 cm in the Adirondacks, on average. Fine and medium roots are still plentiful at this depth but begin to dwindle away to nothing as the spade penetrates to the next layer of soil below, the B2ir-horizon. This is a zone of accumulation in which iron and aluminum, derived from mineral weathering processes above and carried to depth as soluble metal-ligand complexes, finally precipitate as oxides and hydroxides, some crystalline and others paracrystalline or amorphous. The orange-red color reflects the large amount of iron present in this horizon. Few fine to medium roots are found here, mainly because there are fewer nutrients available for plants to feed on. Cementation, resulting from this influx of iron and aluminum and its subsequent precipitation, sometimes results in the development of a fragipan at depth, a hard, almost impenetrable layer in the profile.

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Now down about 50 cm into the forest soil, the B-horizon begins to show a transitional gradient for perhaps another 25 cm to a lighter color, perhaps a light orange changing to a tan or olive-gray. This is the BC-horizon, which, depending upon the sediment type from which the soil evolved, is usually gravelly to sandy because it contains less of the fine-grain weathering products illuviated from above. The bottom of this horizon represents the depth in the Spodosol profile at which no visible signs of chemical alteration are apparent. Below this horizon lies the C-horizon, defined as the original parent material—the glacial sediment —from which, and in which, the soil profile evolved. From the authors’ experience excavating hundreds of soil pits over the past several decades of working in the Adirondacks, a typical Spodosol profile will reach a depth of about a meter, if bedrock does not impede its development. While digging a soil pit, you may encounter boulder-sized rock fragments if the soil developed in till, and a pickax and a crowbar will be necessary for their removal. Soils that developed in outwash sands, on the other hand, are usually devoid of boulders and generally have a sandy, loamy texture and horizons that are more continuous and level.

THE CHEMISTRY AND MINERALOGY OF ADIRONDACK SOIL Spodosols are characterized as naturally acidic, base cation poor soils, and the Spodosols in the Adirondacks are no exception. Acidity is highest in the upper soil horizons, with pH values averaging about 3.7, and lowest in the C-horizons, with pH values averaging about 4.8 (Table 2). Concentrations of exchangeable base cations (i.e., calcium, magnesium, potassium, and sodium loosely bound to organic matter and clay particles) are quite low in Adirondack soils, but are present in sufficient quantities to support a healthy forested ecosystem (Table 2). The cation exchange capacity (CEC) of the soil, which is a measure of the total number of soil exchange sites available for these cations to bind to, typically shows a close correlation with the percent organic matter. Percent organic matter (determined by loss on ignition, LOI) is highest at the surface, drops sharply in the E–horizon, increases somewhat in the Bs/ Bh horizon, and then declines with depth (Table 2). Base saturation, the percent of available exchange sites occupied by base cations, is also highest in the upper horizons where nutrient elements such as calcium are recycled by decomposing plant litter. Recycled elements do not tend to penetrate deeply in the soil so base saturation typically drops to low values at midprofile depths, then increases again toward the C-horizon where exchangeable cations are not mined much by fine roots. Bulk soil chemistry, determined by X-ray fluorescence analysis is commonly interpreted using the dimensionless mass transfer coefficient,

τi, j =

152

Cj, w Ci, p Cj, p Ci, w

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-1

where τ represents the ratio of the concentration of an element of interest (Cj) normalized to an immobile element (Ci ) in the weathered soil (w) and unweathered parent material (p) (Brimhall and Dietrich 1987; Anderson et al. 2002). The τ value is a useful way to compare changes in elemental composition from weathering processes in soils. A τ value of zero indicates an element has not changed from the initial parent composition, whereas a τ value greater than or less than zero indicates addition or depletion of an element relative to the initial parent composition, respectively (Brimhall and Dietrich 1987). Table 2: Average soil chemistry and loss on ignition (LOI) for recent Spodosol profiles sampled at all 21 study sites across the Adirondacks.

Exchangeable Base Cations Average concentration (cmolc /kg)

Horizon

Average Soil pH

Average LOI

3.73

7.07 1.18 0.75 0.13

80.61

3.60

4.00 0.60 0.33 0.11

57.15

3.87

0.30 0.05 0.06 0.09

5.13

3.75

0.58 0.10 0.12 0.13

14.59

B2ir

4.48

0.21 0.03 0.03 0.08

12.19

4.49

0.40 0.04 0.04 0.08

8.83

4.77

0.25 0.02 0.02 0.07

4.88

4.76

0.09 0.01 0.01 0.07

2.51

Mineral weathering is most intense in the upper horizons of Adirondack soil profiles, where organic acids are constantly being produced and are reacting with minerals there. Acid is used by these reactions so soil water becomes increasingly more neutralized as it percolates deeper through the soil profile. As can be seen in Figure 3, most elements are depleted within the soil profile. Exceptions to note are calcium, which is highly enriched in the organic horizon from the release of plant-bound calcium in decomposing litter, and iron, which is transported down-profile and accumulates in the B-horizon. All elements show their greatest depletion in the E–horizon, an organic-poor eluviated zone, increasing in concentration to the levels of the unweathered parent material at depth. The lower depletion values above the E-horizon reflect additions of recycled cations from above by decomposing vegetation. It should be noted here that for the past century acid deposition has delivered strong acids (i.e., sulfuric and nitric) to the forest floor, intensifying weathering in the upper soil horizons, and, as shall be discussed later, causing problematic depletion of nutrient cations.

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Figure 3: Representative Tau plot depicting enriched and depleted elements in an Adirondack Spodosol profile. Depth of the profile is approximately 100 cm.

Mineral abundances in Adirondack soils vary depending on location and the nature of the regional bedrock, which in turn influences the composition of the parent glacial sediment from which soil minerals are inherited (Newton et al. 1987). Silicate minerals dominate in Adirondack soils, and as previously mentioned, quartz and the feldspars are ubiquitous and are most abundant. In those locations where carbonate minerals are present in the bedrock, such as in the marble belts near Newcomb in the central Adirondacks or in the calcsilicatebearing metasedimentary rocks around Bug Lake and Windfall Pond in the southwestern Adirondacks, traces of calcite are occasionally found in the deepest soil samples (Harstad and Newton 1983). More often, the calcite has long ago dissolved in the highly acidic soil, and the only remnant of its former presence may be higher concentrations of soil exchangeable calcium. The general stability of silicate minerals in acidic soils is fairly well known, with those formed at high temperatures and pressures and containing elements such as magnesium, iron, and calcium more susceptible to weathering than those formed at low temperatures and pressures and containing elements such as potassium and sodium (White 1995; White et al. 1996). For example, calcium-rich plagioclase will weather faster than sodium-rich plagioclase, and both will weather faster than potassium feldspar (Kolka et al. 1996). Hornblende, a silicate mineral rich in calcium and magnesium, can constitute up to 50 wt%

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or more of the heavy mineral fraction (specific gravity >2.96) of Adirondack Spodosols (April et al. 1986a). April and Newton (1983) showed that concentrations of hornblende can drop from 6 wt% in the C-horizon to zero in the upper few centimeters of Adirondack soil profiles, where chemical weathering is most intense. The congruent weathering and dissolution of hornblende, as well as the weathering of other accessory minerals such as diopside and biotite, both rich in nutrient base cations, was observed in SEM analyses of soil samples collected from the central Adirondacks (April and Newton 1992). It is important to note here that in Adirondack Spodosols, with relatively low fertility and low availability of nutrient cations for plant growth, the weathering of accessory minerals provides a disproportionately large fraction of nutrient cations to soil exchange sites compared to their low abundance in the soil (April et al. 1986b). Without minerals like hornblende, diopside, and biotite providing nutrient base cations such as Ca2+, Mg2+, and K+, and apatite providing phosphorus, Adirondack soils would be less able to support a healthy forested ecosystem. But, can the weathering of these silicate minerals supply nutrient base cations at a pace that keeps up with the demand of a healthy forest ecosystem? Historically, it appears that this has been the case. But, as we shall see, anthropogenic influences that disturb the delicate balance of natural ecosystems can cause problems. Lastly, it is worth noting that secondary weathering products formed during pedogenesis, such as oxides and hydroxides of iron and aluminum, and clays, such as vermiculite, smectite, and kaolinite, are also common minerals in Adirondack Spodosols (April et al. 1986a). Johnson and McBride (1989) identified microcrystalline goethite, ferrihydrite, and imogolite-like material, too poorly crystalline to be considered true imogolite because it lacked characteristic tubular morphology. As for the clay minerals, vermiculite is ubiquitous in Adirondack Spodosols, forming from the weathering and transformation of biotite and muscovite. Studies of the secondary clay products in soil and glacial deposits from forested sites across the Adirondack Mountains show that the up-profile mineral weathering sequence of mica to mixed-layered mica-vermiculite to vermiculite to low-charge vermiculite (April and Newton 1983; April et al. 1986a) progresses even further in some locations to form smectite in the uppermost soil horizons (April et al. 2004). As these clays weather, they release potassium and magnesium to the soil system. The swelling clays vermiculite and smectite also provide exchange sites for storing nutrient cations and interlayer sites that accommodate water molecules.

ACID RAIN AND SOIL ACIDIFICATION A century of acid deposition has resulted in changes to soil, soil water, and surface water chemistry in the Adirondack Mountains. Although deposition of both sulfuric and nitric acids has decreased substantially over the past three decades as the Clean Air Act Amendments of 1990 and the Acid Rain Program (1995-2010) prescribed, even with implementation of more recent programs to ameliorate air pollution (e.g., the NOx Budget

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Trading Program [2003-2009]; the Clean Air Interstate Rule [2010-2015]; and the CrossState Air Pollution Rule [2015]), lingering effects of acid rain remain in lake and forest ecosystems (EPA 2013). Acidified lakes and streams, both chronic and episodic, continue to persist. However, there are indications that some lakes and streams are showing signs of recovery, with pH and acid neutralizing capacity (ANC) values drifting slightly higher (Driscoll et al. 2007; Waller et al. 2012; Strock et al. 2014). In Adirondack soils, levels of aluminum and soil acidity have increased over time (Warby et al. 2009). Concomitantly, depletion of exchangeable base cations, especially calcium, which is so critical for plant growth, also has occurred, and base saturation, in general, has declined (Bedison and Johnson 2010). The depletion of calcium from soil may delay the recovery of ANC values in acidified surface waters (e.g., Warby et al. 2005). Whether the rate of chemical weathering of primary minerals in soil is enough to resupply nutrient base cations to exchange sites has yet to be determined. It may take decades, perhaps many, before mineral weathering reverses the effects of soil acidification that has occurred over most of the past century. To better demonstrate how decades of acid deposition has affected soils in the Adirondacks, briefly presented below are two case studies—one that investigated changes in soil chemistry over time and a second that monitored the effects of liming on soil chemistry.

Figure 4: Location of the 21 watersheds from which samples were collected in 1979, 1982-1983, and 2005-2006 for the “Cation Depletion” case study and the location of the “Town of Webb” sites where the “Soil Liming” case study was conducted.

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CASE STUDY 1: CATION DEPLETION IN ADIRONDACK SOILS Because Spodosols naturally have low base saturation, leaching of base cations by acidic inputs exacerbates an already fragile balance between nutrient supply for vegetation and organisms that live on or within the forest floor, and replenishment of these nutrient cations by litter decay and mineral weathering (atmospheric inputs) are minimal. In 2005, a study to determine changes in Adirondack soil chemistry over a period of approximately two decades was undertaken by comparing the chemical characteristics of newly collected soil samples with those of archived soil samples collected from the same lake-watershed sites (Figure 4) approximately two decades earlier (1979 and 1982-1983) (April and Newton 1983; Newton et al. 1987; Goldstein et al. 1987). Particular attention was paid to determining differences in exchangeable calcium and percent base saturation, both of which were reported in previous studies to show significant declines over time in soils of forested ecosystems in the northeastern U.S. (Lawrence et al. 1997; Sullivan et al. 2006).

Exchangeable Base Cations A significant decrease of exchangeable Ca in the uppermost horizons of Adirondack soil profiles was observed over the period of study (Table 3 and Figure 5). Rondaxe watershed shows the highest average percent decrease in Ca in Oa-horizons, from a mean of 8.6 cmolc kg -1 to 0.6 cmolc kg -1, a drop of 8.0 cmolc kg -1 or almost 93%. Smaller, yet significant, decreases in exchangeable Ca are seen in the Oa-horizons of all ten other sites as well. Except for Russian and Sagamore watersheds, exchangeable Mg also shows declines in mean values for Oa-horizons over the period of study (Table 3). Exchangeable K and Na show no definitive trends over time because concentrations of these cations are quite low to begin with (K < 1.0 cmolc kg-1 and Na < 0.1 cmolc kg -1) (Table 3). Table 3: Changes in exchangeable base cations Ca, Mg, K, and Na over two decades in Oa-horizons from eleven representative sites across the Adirondacks.

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Figure 5: Average change in exchangeable calcium over two decades at eleven representative sites across the Adirondacks. The greatest depletion of calcium occurs in the Oa-horizon at all sites.

Figure 6: Average base saturation by horizon for archived and recent samples collected from the 21 study sites. Base saturation decreased over time due to cation depletion.

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Base Saturation and Exchangeable Acidity Percent base saturation decreased in all horizons of Adirondack soils over the period of study, with the greatest change occurring in the uppermost soil horizons (Figure 6). Decreases in base saturation are caused by base cations being leached from exchange sites and replaced with H+ from strong acids (acid rain) and with monomeric aluminum (Al3+) derived from mineral weathering. One effect of soil acidification has been to increase the mobility of monomeric aluminum, a potential toxin linked to fish mortality and forest decline (Godbold 1988; Cronan and Schofield 1990; Cronan and Grigal 1995). Overall, the study showed calcium depletion, and, to a lesser extent, magnesium depletion in the uppermost soil horizons of the Adirondack Mountains over a period of approximately two and a half decades. These changes to soil chemistry are most noticeable in Oa-horizons but can reach depths of up to 25 cm. Results of this study are consistent with other studies of soil chemical changes in the northeastern U.S. Warby et al. (2009) found that organic soils (Oa-horizons) across the northeastern U.S. continued to acidify even though significant decreases in sulfate (SO42-) and hydrogen ion (H+) deposition has occurred across the region (Driscoll et al. 2003; Kahl et al. 2004). Sullivan et al. (2006, 2007) found that acidic deposition depleted soil-base cation pools and that, despite CAAA mandated cuts in air pollution, continued leaching of cations may restrict the extent to which acidified lakes and streams recover in the future. Loss of soil calcium could hinder the recovery of the acid neutralizing capacity (ANC) of surface waters, especially for those lakes and streams that have remained chronically acidic and are located in watersheds underlain by thin till and granitic bedrock, and where surface water ANC values are less than 25 Âľequiv L-1 (Warby et al. 2005). Finally, calcium depletion may negatively impact forest health and productivity for years to come (Lawrence et al. 1997; Shortle et al. 1997; Bailey et al. 2004; Schaberg et al. 2006; Sullivan et al. 2013). There is still a lot to be learned about the long-term effects of low base saturation and increasing exchangeable acidity on this fragile Adirondack forest soil and the biotic community it supports.

CASE STUDY 2: SOIL LIMING As another aspect of the 2005 study, a total of 1.6 tonnes of limestone powder (98.5% CaCO3) was applied, in two equal applications (half in 2005 and half in 2006), to each of four forested sites in the southwestern Adirondacks near Old Forge, NY (Town of Webb). Each site was divided into two circular plots (22.5 m radius), a control plot that was not limed and an experimental plot treated with the calcium carbonate. One of the objectives of this liming study was to monitor whether the calcium released by the dissolution of the lime over time replaced exchangeable soil calcium that had been depleted by decades of acid rain. Prior to liming, soil samples from pits excavated in both the control and experimental plots at the four sites were collected and analyzed for pH, base cations, and base saturation.

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pH and Soil Acidity: Ten years later The soil pH of both the limed and control sites ten years later are shown in Figure 7. Below 20 cm, soil pH values for both the limed and unlimed control plots are about the same, averaging approximately 4.2. Above 20 cm, soil pH values steadily decline to an average of 3.5 in the unlimed control plot, a value typical for the acidic O- and E-horizons of soil in the Adirondacks, but soil pH values rise to an average of 6.3 in the limed plot, responding to the neutralizing capacity of the dissolved calcium carbonate.

Exchangeable Calcium and Base Saturation: Ten years later The amount of exchangeable calcium is higher by more than ten-fold near the soil surface in the limed sites compared to the unlimed control sites and remains consistently higher down to a depth of 35 cm (Figure 8). A simple calculation reveals that over the 10-year period following liming, calcium translocated down profile at a rate of ~3.5 cm/yr, to a depth well beyond the rooting zone of most vegetation. In addition, exchangeable magnesium values also are higher in the upper 10 cm of the limed sites, which is not surprising as chemical analysis of the powdered limestone revealed that it contains about 1.0 wt% MgCO3 (Figure 8). Exchangeable potassium and sodium show similar values for both the limed and unlimed plots, indicating that the lime had no effect on the concentration of these base cations. Base saturation is 20% to 40% higher in the limed sites throughout the soil profile and reaches 100% in the upper 10 cm of the amended soils. In addition, base saturation in the limed soils remains above 50% down to a depth of ~30 cm compared to a depth of only ~15 cm in the unlimed plots (Figure 8). In a companion study of the biota, McCay et al. (2013) found that invertebrate populations differ markedly in limed versus unlimed plots, with snails increasing in abundance and millipedes and spiders decreasing in abundance in the limed plots. The decrease in millipedes, especially, may have contributed to the reduction in the rate of litter decay in limed plots. Results of this study suggest that amending soil with lime can modify soil chemistry rather quickly and dramatically by raising soil pH to near neutral values, by replacing exchangeable calcium and magnesium depleted by soil acidification, and by increasing base saturation. Watershed and lake liming are expensive undertakings, however, but aside from providing benefits that counteract the effects of acid deposition, liming has been linked to some detrimental effects on biota that inhabit these ecosystems and normally thrive in calcium-poor and less alkaline environments. (Smallidge 1993; Moore 2014).

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Figure 7: Average soil pHw in limed and unlimed plots after 10 years.

Figure 8: Average exchangeable calcium, magnesium and base saturation in limed and unlimed plots after 10 years.

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SUMMARY How long it will take for the acidified systems of the Adirondacks to recover from a century of acid deposition? This is a question no one can answer with certainty—not yet, anyway. Once such a fragile and complex ecosystem as the Adirondacks is altered by anthropogenic activities, it is difficult to project what will become of it, for nothing like this has ever happened before. When will acidified lakes return to their historical pH and ANC values? Will fish species decimated by aluminum toxicity reestablish old habitats, and if so, when? How long will it take for mineral weathering in soils to replenish depleted nutrient base cations necessary for the maintenance of a healthy forest ecosystem? When will the populations of terrestrial biota affected by changes in soil chemistry and changes in the proportions of species at different points in the food chain recover to historical norms? Unfortunately, we do not even know precisely what the “historical norm” was, because the natural state of the Adirondack ecosystem prior to the early part of the 20th century, before the onset of acid deposition, is largely unknown. Fortunately, scientists are monitoring the health of the Adirondack forests and lakes and there are some promising signs. Lawrence et al. (2015) found that the acidification of forest soils is finally beginning to show a reversal, and Strock et al. (2014) measured a recent acceleration in the rate of recovery of lakes as acidic deposition in the northeastern U.S. declines. Josephson et al., (2014) measured a slight, but definite, increase in phytoplankton abundance in Honnedaga Lake and also noted the persistence of the brook trout population, but they state that further recovery will likely be slow. Trout have begun a resurgence in other lakes in the Adirondacks (Mitchell 2014) as well, as have chrysophyte and diatom species in Big Moose Lake (Arseneau et al. 2011). While this is all good news, a recent study by Bishop et al. (2015) alerts us to the worry that sugar maple (Acer saccharum) is showing symptoms of stress and elevated mortality rates across the Adirondacks – all the more reason for scientists to remain vigilant and to continue monitoring the health of the Adirondack ecosystem over time. Let us hope that the recovery continues and that the deleterious effects of almost one hundred years of acid deposition over the Adirondack Mountains vanish over our lifetime. ACKNOWLEDGEMENTS

Research was funded by the National Science Foundation (DBI-0442222 and EAR 0725019). Thanks to the Town of Webb for permission to conduct studies on town land and to students Ashlynne Rando, Lauren Frisch, and others who assisted with sample collection and laboratory analyses over the years. A.R. and L.F. conducted some of the case study work presented as part of their senior thesis. Thanks to J. Chiarenzelli, who reviewed our manuscript.

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L I T E R AT U R E C I T E D

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Cronan, C.S. and D.F. Grigal. 1995. “Use of calcium/aluminum ratios as indicators of stress in forest ecosystems,” Journal of Environmental Quality, 24: 209-226. Driscoll, C.T, K.M. Driscoll, M.J. Mitchell and D.J. Raynal. 2003. Effects of acidic deposition on forest and aquatic ecosystems in New York State. Environmental Pollution, 123: 327-336. Driscoll, C.T., K.M. Driscoll, K.M. Roy, and J. Dukett. 2007. “Changes in the chemistry of lakes in the Adirondack region of New York following declines in acidic deposition, Applied Geochemistry, 6: 1181-1188. EPA. 2013. “2013 Program Progress – Clean Air Interstate Rule, Acid Rain Program, and Former NOx Budget Trading Program.” Accessed January 2016 from http://www.epa.gov/ airmarkets/programs. Godbold, D.L., E. Fritz, and A. Huttermann. 1988. “Aluminum toxicity and forest decline,” Proceedings of the National Academy of Sciences, 85: 3888-3892. Goldstein, R., S. Gherini, C. Driscoll, R.H. April, C. Schofield, and C. Chen. 1987. “Lake-watershed acidification in the North Branch of the Moose River: Introduction,” Biogeochemistry, 3 (1-3): 5-20 (special issue). Harstad, L. and R. Newton. 1983. “Geologic controls on the sensitivity of Woodruff Pond to acidification.” Proceedings of the Second New York State Symposium on Atmospheric Deposition, October 1983, Albany, NY. Johnson, M.G. and M.B. McBride. 1989. “Mineralogical and chemical characteristics of Adirondack Spodosols: evidence for para- and non-crystalline aluminosilicate minerals,” Soil Sciences Society of America Journal, 53(2): 482-490. Josephson D.C., J.M. Robinson, J. Chiotti, K.J. Jirka, and C.E. Kraft. 2014. “Chemical and biological recovery from acid deposition within the Honnedaga Lake watershed, New York, USA,” Environmental Monitoring and Assessment, 186(7): 4391-409. Kahl, J. S., J.L. Stoddard, R. Haeuber, S.G. Paulsen, et al. (+12). 2004. “Have U.S. surface waters responded to the 1990 Clean Air Act Amendments?” Environmental Science and Technology, 12(15): 485-490. Kolka R.K., D.F. Grigal, E.A. Nater. 1996. “Forest soil mineral weathering rates: use of multiple approaches,” Geoderma, 73: 1-21. Lawrence, G.B. M.B. David, S.W. Bailey, and W.C. Shortle. 1997. “Assessment of soil calcium in red spruce forests in the northeastern United States,” Biogeochemistry, 38: 19-39.

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Lawrence, G.B., P.W. Hazlett, I.J. Fernandez, R.Ouimet, S.W. Bailey, W.C. Shortle, K.T. Smith, and M.R. Antidormi. 2015. “Declining Acidic Deposition Begins Reversal of Forest-Soil Acidification in the Northeastern U.S. and Eastern Canada,” Environmental Sciences and Technology, 49: 13103-13111. Logan, W.B. 1995. Dirt, the Ecstatic Skin of the Earth. New York: Riverhead Books. McCay, T.S., C. Cardelus, and M.A. Neatrour. 2013. “Rate of litter decay and litter macroinvertebrates in limed and unlimed forests of the Adirondack Mountains, USA,” Forest Ecology and Management, 304: 254-260. Mitchell, L. 2014. “Coming Full Circle,” New York State Conservationist, August 12-15, 2014. Moore J-D., R. Ouimet, R.P. Long, and P.A. Bukaveckas. 2014. “Ecological benefits and risks arising from liming sugar maple dominated forests in northeastern North America,” Environmental Reviews, 23(1): 66-77. Newton, R.M., J. Weintraub, and R.H. April. 1987. “The relationship between surface water chemistry and geology in the North Branch of the Moose River,” Biogeochemistry, 3(1-3): 21-35 (special issue). NRCS. 1999. Soil Taxonomy A Basic System of Soil Classification for Making and Interpreting Soil Surveys. United States Department of Agriculture, Agriculture Handbook Natural Resources Conservation Service Number 436. Richter D.D. and D. Markewitz, 1995. “How deep is soil?” BioScience, 45(9): 600-609. Schaberg, P.G., J.W. Tilley, G.J. Hawley, D.H. DeHayes, and S.W. Bailey. 2006. “Associations of calcium and aluminum with the growth and health of sugar maple trees in Vermont,” Forest Ecology and Management, 233: 159-169. Shortle W.C., K.T. Smith, R. Minocha, G.B. Lawrence, and M.B. David. 1997. “Acidic deposition, cation mobilization, and biochemical indicators of stress in healthy red spruce,” Journal of Environmental Quality, 26: 871-876. Smallidge, P.J., A.R. Brach, and I.R. Mackun. 1993. “Effects of watershed liming on terrestrial ecosystem processes,” Environmental Reviews, 1(2): 157-171. Strock, K.E., S.J. Nelson, J.S. Kahl, J.E. Saros, and W.H. McDowell. 2014. “Decadal Trends Reveal Recent Acceleration in the Rate of Recovery from Acidification in the Northeastern U.S.” Environmental Science and Technology, 48: 4681-4689. Sullivan, T.J., I.J. Fernandez, A.T. Herlihy, C.T. Driscoll, T.C. McDonnell, N.A. Nowicki, K.U. Snyder, and J.W. Sutherland. 2006. “Acid-base characteristics of soils in the Adirondack Mountains, New York,” Soil Sciences Society of America Journal, 70: 141-152.

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Sullivan, T.J., B.J. Cosby, A.T. Herlihy, C.T. Driscoll, I.J. Fernandez, T.C. McDonnell, C.W. Boylen, S.A. Nierzwicki-Bauer, and K.U. Snyder. 2007. “Assessment of the extent to which intensively-studied lakes are representative of the Adirondack region and response to future changes in acidic deposition,” Water, Air, and Soil Pollution, 185: 279-291. “Effects of acidic deposition and soil acidification on sugar maple trees in the Adirondack Mountains, New York,” Environmental Science and Technology, 47(22): 12687-12694. Waller, K., C. Driscoll, C., J. Lynch, D. Newcomb, and K. Roy. 2012. “Long-term recovery of lakes in the Adirondack region of New York to decreases in acidic deposition,” Atmospheric Environment, 46: 56-64. Warby, R.A.F. and C.T. Driscoll. 2005. “Chemical recovery of surface waters across the northeastern United States from reduced inputs of acidic deposition: 1984-2001,” Environmental Science and Technology, 39 (17): 6548-6554. Warby, R.A.F., C.E. Johnson, C.T. Driscoll. 2009. “Continuing acidification of organic soils across the northeastern USA: 1984-2001,” Soil Sciences Society of America Journal, 73(1): 274-284. White A.F. 1995. “Chemical weathering rates of silicate minerals in soils,” in A.F. White and S.L. Brantley (Eds.), Reviews in Mineralogy and Geochemistry, 31: 407-459. White, A.F., A.E. Blum, M.S. Schulz, T.D. Bullen, J.W. Harden, and M.L. Peterson. 1996. “Chemical weathering rates of a soil chronosequence on granitic alluvium: I. Quantification of mineralogical and surface area changes and calculation of primary silicate reaction rates,” Geochimica et Cosmochimica Acta, 60(14): 2533-2550.

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ADIRONDACK LANDSLIDES: HISTORY, EXPOSURES, AND CLIMBING KEVIN B. MACKENZIE

St. Lawrence University, 23 Romoda Drive, Vilas 117B, Canton, NY 13617, 315.229.5067, kmackenzie@stlawu.edu or mudrat@adirondackmountaineering.com

KEYWORDS:

Adirondack Slides, Tropical Storm Irene, Landslides, Landslide History

ABSTRACT Rock, soil, and vegetation avalanche down the slopes of the Adirondack Mountains, especially the High Peaks, on a regular basis. These landslides occur most often in response to heavy rainfall events and saturated conditions. The first guides and explorers used slides as the path of least resistance en route to various summits. Some slides have received considerable interest because of their recreational potential, location and accessibility, recent activity, or the well exposed geological features they contain. Tropical Storm Irene struck the region on August 28, 2011. It wreaked havoc on local communities, as well as, many areas of the backcountry. The deluge triggered over forty significant slides and countless minor ones, some of which are easily accessible. It thus opened up slide climbing to a wider audience and provided exceptional bedrock exposures for geoscientists interested in the Adirondack Region. The text below incorporates a short history of the slides and a sample of the more interesting Irene-related slides.

INTRODUCTION Hurricane Irene made landfall in the United States as a Category 1 hurricane. The storm was down-graded to a tropical storm by the time the heaviest rain bands reached the Adirondacks on August 28, 2011. It was not the wind but the large volume of precipitation

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over an afternoon that caused the most damage. Amounts totaled 7.55 inches on Whiteface Mountain (Stanne 2012) and up to 10 inches (in) in Keene (based on reports from local residents). I will focus my discussion on the eastern High Peaks (Figure 1) where the impact was greatest (Brown 2011). This event had real implications for me and my wife, and we observed the East Branch of the Ausable River rise nearly a meter (m) in a few minutes. As a consequence, mature pine trees and propane tanks were removed from residents’ yards and collided with the Route 73 bridge in Upper Jay. The Ausable crested over 3.35 meters (11 feet [ft]) above flood stage. It is estimated that the storm resulted in 62 billion gallons of water entering the Ausable River watershed due to rainfall totals exceeding 25.4 centimeters (cm; 10 in) (Brown 2011). The water removed culverts, undermined roads, damaged bridges, and destroyed buildings. Damage from flooding in the nearby villages of Keene, Keene Valley, and Upper Jay was staggering. Trees with their root systems intact were torn from riverbeds and deposited on Route 73. Houses were shifted from foundations or flooded. Normally a small mountain stream, Styles Brook, carried a cabin downstream and lodged it under a bridge between Upper Jay and Keene. Governor Andrew Cuomo requested a major disaster declaration on August 28, 2011. Figure 1: Location of historic and recent landslides mentioned in Table 1 and text. Numbers refer to Table 1. Background is a shaded relief map of the High Peaks Region. Village abbreviations include: AF – Ausable Forks; E – Elizabethtown; J – Jay; K – Keene; KV – Keene Valley; LP – Lake Placid; SL – Saranac Lake; T – Tahawus; W - Wilmington. Inset shows location of high peaks (grey rectangle) with respect to the Adirondack Park (dark) and boundary (blue).

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Irene’s greatest affects were felt on the afternoon of August 28, 2011; it was short in duration but extreme in intensity. Its effects were historically unprecedented and likened to a 100year flood by many residents. The following days were chaotic and heartbreaking as the destruction of the event was fully realized and the scale of the human tragedy became apparent. Tropical Storm Irene’s impact on the towns and villages has been well documented by the media, but the changes to the backcountry were also extensive. In response, the Department of Environmental Conservation closed portions of the backcountry to assess the damage soon after the storm. These included the Giant Mountain Wilderness Area, Dix Mountain Wilderness Area, and the Eastern High Peak zone. Most were opened again by mid-September. Over the following months the infrastructure of the backcountry was slowly repaired: trails rerouted, ladders fixed, and bridges rebuilt. It was decided that breached dams at Duck Hole and Marcy Dam would not be repaired and that some trails, such as, the Southside Trail along Johns Brook would no longer be maintained. In the weeks and months that followed, aerial photographs posted on the internet showed some of the changes to the Eastern High Peaks. There were a striking number of slides reported, yet photographers only captured a subset of them. My interest began as a simple question, “Which slides were new and which remained unmodified?” Figure 2 shows several slides triggered during Irene. Basin Mountain’s Northeast Shoulder slide dominates the photo. Slides on Algonquin Peak, Wright Peak, and a ridge of Saddleback Mountain also show new activity. Figure 2: A new landscape formed during Tropical Storm Irene. The 2011 slides are the lighter strips. Photo by author.

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Gratefully no one died from the slides associated with Tropical Storm Irene. However, an article describing the “great flood” of 1830 in an 1872 issue of the Plattsburgh Republican was written by the mountain guide Orson Schofield Phelps. The opening paragraphs describe scenes that were similar to those that occurred during Tropical Storm Irene. The latter half of the article describes a slide and its effect on a local family. Phelps wrote of incessant rains continuing for nine days washing away houses, business, and bridges. On the ninth day, a slide triggered in the Walton Brook Basin (44°13’49.4”N, 73°49’56.4”W) – the Walton slide. It killed a member of the Walton family, one of two brothers who lived near the brook. His wife, Lucy, was caught in the debris and survived for a time. She reportedly succumbed to injuries sustained during the event two years later (Phelps 1872). The article is a testament to the ever-changing nature of the landscape and to the powerful forces that sculpt it both slowly and during extreme weather events. Only remnants of the slide remain today, proof that nature reclaims even the most disrupted terrain and heals over time.

CHARACTERISTICS OF SLIDES IN THE ADIRONDACK HIGH PEAKS Slides or debris avalanches like the Walton slide occur with some regularity; one might say frequently in terms of geologic time (see Table 1). History shows that they are generally triggered by intense precipitation falling over a short period of time (localized downbursts/ hurricanes) or heavy rainfall over several days, thoroughly saturating the soil. The range of precipitation intensity varies from 10 cm in one hour to 56 cm over two days (Bogucki 1977). When the thin layer of soil covering the underlying bedrock becomes saturated on an area of sufficient slope, gravity can exceed frictional forces and slippage can occur, sometimes catastrophically. Soil, trees, and rocks can slide downhill at an amazing speed. Debris avalanches are most likely to occur on slopes between 17° and 44° though most form on slopes > 30° (Bogucki 1977). Small stream valleys or gullies draining higher elevations of sufficient slope seem especially susceptible to sliding. Existing slides are often augmented in length, width, or in the number of converging slide tracks near their head walls, generally following the course of small tributaries or intermittent gullies. As discussed below, these additions to pre-existing slides commonly occur and, even if the change is significant, are not technical “new” slides but repeat offenders. Slides distinctly separated from a neighboring track are generally described as “new,” but an intriguing question is – are they truly new or simply a modern incarnation of an ancient landslide? Tim Tefft suggests that the Lake Placid slide (44°21’55.1”N, 73°54’26.1”W) has probably re-occurred over thousands of years (Tefft 2011). If true, this puts “new” in a subjective context and accurate only when related to a human lifespan or initiation of settlement. For simplicity’s sake, I will continue using the term if a slide is distinct and not an enlargement of an existing slide, though “reactivated” may be a more accurate descriptor in most cases.

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Historic photographs and aerial photographs also confirm that slides often reoccur in the same areas. Resources such as Google Earth aid with navigation as well as provide a limited set of historic aerial photographs. The timeline feature provides incremental imagery back to the 1990s. The pattern of trees on mountainsides and regrowth in disrupted streambeds indicate that landslides scars can gradually revegetate. Comparing photographs of recent slides to older images of the same area sometimes show the new slide located in roughly the same area as an older slide. The Lobster Claw slide (44°4’29.6”N, 73°46’55.2”W) located on the western aspect of the ridge between Dix Mountain and Hough Peak is a good example of a recurrent slide. It was created after Tropical Storm Irene during the early summer of 2013 as a result of heavy rains.

POST-SETTLEMENT HISTORY OF ADIRONDACK SLIDES It is no secret that the easiest way to climb a mountain is via the path of least resistance. The slides provide such a path. While they may be precarious, ascending one is generally easier than bushwhacking through stiff, tightly woven evergreens that top the summit of many of the High Peaks. Following a stream to higher elevation often provides access to slides. The earliest guides and explorers—Phelps, Colvin, and Nye—used this to their advantage. The first trail to Mt. Marcy’s summit was cut from the southeast by the guide Orson Schofield Phelps in 1861. It ascended from Panther Gorge between Marcy and Haystack to Marcy’s “great slide” (now called the Old Slide [44°6’24.7”N, 73°55’13.3”W]) on its southern aspect. The slab, though steep with some sections approaching 45° or more, effectively bridged the gap between the Skylight/Marcy drainage stream and Marcy’s ridge. Russell M.L. Carson writes in Peaks and People of the Adirondacks that the trail “was eventually abandoned for a new route selected by Colvin, August 28, 1873.” Trails are generally a safer option than climbing a slide; particularly when transporting heavy equipment such as that used for the initial surveys or during inclement weather. On the southern face of Whiteface Mountain, we find another early trail that incorporated a slide, the Lake Placid slide, whose long gray path can still be seen from the village of Lake Placid. By most accounts, this formed (or more likely was enlarged) in the early 1800s. The generally low-angle southwest-facing scar comprised the final section of the first trail cut from Lake Placid around 1865 by Bill Nye (Hayes 1928). This too was abandoned when an alternative trail was cut. Mt. Colden is one of the most slide-torn mountains of the High Peaks with tracks on nearly all of its aspects. Figure 4 shows a large concentration of slides on Mount Colden’s northwestern flank. Adirondack surveyor Verplanck Colvin was descending Whiteface Mountain on August 20, 1869 during a thunderstorm that he described as one that “had not occurred for very many years” (Colvin 1869). Soon after, he learned of changes to Avalanche Lake at the foot of Mt. Colden. The Trap Dike, a large eroded gabbroic dike about 30 m

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(100 ft) deep and over 18 m (60 ft) wide, was cleaned out. This was likely the birth or an enlargement of the Colden slide (44°7’50.1 N, 73°57’51.3”W), the largest slide that intersects the Trap Dike. It was the classic exit for those climbing the Trap Dike until 2011. Colvin’s description of the denuded cleft bears a striking similarity to the changes wrought by Tropical Storm Irene. Figure 3: Mount Colden’s slide-torn northwestern aspect above Avalanche Lake. Photo by author..

A new slide formed on the western side of the Sentinel Range during July of 1932. “The slide began in a narrow wash not more than 15 ft wide and created the present denuded strip which is over 400 yards long” (Lake Placid News 1932). Two parties explored the slide within a week and described it as primarily a landslide as opposed to rockslide. Six years later in the summer of 1938, several days of rain created a slide on the southsoutheastern flank of Wright Peak (West 1940). Ranger Alton C. West climbed it soon after. He vividly described both how it was formed and the destruction he encountered. It has grown in at the base but still remains a popular slide climb known as the Left Wing Airplane slide (44°8’59.6”N, 73°58’42.0”W), in reference to a B-47 bomber that crashed into the peak during January of 1962. Pieces of the wreckage are strewn on the slide, both sides of the summit ridge, and on the summit proper. The Right Wing slide formed years later about 200 m (650 ft) to the east. Wright Peak is also known for three additional slides on its northeastern aspect – the Angel slides (44°9’18.3”N, 73°57’59.1”W). There are three in the set; two formed in 1999 and one in 2011.

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One of the most notable slide arrays to both the casual observer and for the slide climbing community was enlarged after a localized cloudburst over Giant Mountain on June 29, 1963. Local climber Jim Goodwin reported eleven new or enlarged slides in the Fall/Winter 1963/64 issue of Peeks magazine. Activity was reported on the western cirque, northeastern and southeastern slopes, and on the ridge above Putnam Brook. The western cirque slides quickly gained popularity. The Eagle (44°9’33.8”N, 73°43’21.1”W) and Bottle (44°9’45.3”N, 73°43’31.5”W) slides are still classic climbs. In the valley below, Roaring Brook trapped several cars in floodwaters, gravel, and mud as it overflowed its banks (Joplin 2013). Slides along Roaring Brook, Giant Mountain, and above Roaring Brook Falls created additional exposures of an intrusion breccia first noted by Kemp (1921) and of considerable geologic interest (deWaard 1970; McLelland et al. 2016). Hurricane Gloria moved over the region in 1985 and left Santanoni Peak with the 1.6 km (1 mi) long Ermine Brook slide (44°4’12.4”N, 74°8’42.7”W) on its southwestern flank. It was one of the longest slides at 1.6 km (1 mi) until 2011. While it has grown in over the years, it is a worthwhile, if not remote, scramble with a 17.7 km (11 mi) approach. Tropical Storm Floyd then struck the region on September 16, 1999. It brought heavy rains and destructive winds that created widespread blowdowns. The precipitation triggered over a dozen slides, some destined to become slide climbing and ski mountaineering classics. Several were enlarged by Tropical Storm Irene. These accounts are only a few examples of the myriad slides created over the years. Table 1 provides available information on slides that date back to the early eighteen hundreds. Table 1: Information on historic and modern landslides in the Adirondack Region. Exact dates are noted when known. All slides listed are significant in length (>152.4 m [500 ft]). Neither the dates nor slide list are meant to be all-inclusive. Rather they are meant to demonstrate that the mountains are in a continual state of flux. Other weather events such as floods during 1864, 1893, and 1924 each involved sufficient precipitation to wash away bridges and cause extensive damage to the region. It is safe to conclude that slide activity accompanied many unlisted events. DATE OF CHANGE

MOUNTAIN NAME SLIDE ASPECT

SLIDE EXAMPLE(S) NUMBER ON FIGURE 1

TRIGGER

REFERENCE

1808 Whiteface, SW 1) Lake Placid slide n/a

(Chilson, George, Tucker, and Wheeler 2003)

1830

(Watson, 1869; Phelps, 1872; Konowitz 2011)

Cascade, NW; Porter Mtn. Ridge, NE; Big Slide, S

2) Cascade slide 3)Walton slide 4) Main face of Big Slide Mtn.

Nine days of heavy rain

1856, 9/30 Gothics, SE 5) Slide on “East” Face Heavy rain

(Arnold 2011; Chilson, George, Tucker, and Wheeler 2003)

1869, 8/20 Colden, NW 6) Colden slide

(Colvin 1869)

1932, 7/30 or 7/31

Kilburn, W

Heavy rain

(Lake Placid News 1932)

1938, Sum. Wright, SSE 7) Left Wing slide

“Great Hurricane” of 1938

(West 1940)

1942, Sept. Colden, NW 8) One or more western

Rainfall face slides

(Ticonderoga Sentinel 1942)

1947

Hurricane

(Eagan 2011)

Macomb, W

n/a

Thunderstorm (or enlargement)

9) Multiple

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DATE OF CHANGE

MOUNTAIN NAME SLIDE ASPECT

1950 Macomb, W

SLIDE EXAMPLE(S) NUMBER ON FIGURE 1

TRIGGER

REFERENCE

10) Macomb slide Hurricane (Eagan 2011) (into Slide Brook)

1963, 6/29 Giant, Rocky Peak 11) >12 Slides including: Ridge, Multiple/ Eagle, Bottle, Tulip, Question Each Peak Mark,, Finger, Dipper, East Face (enlarged), NE slides, Putnam Brook slides

Isolated downburst

1969, 8/17 (est.)

n/a

(Healey 1969)

1970 Dix, W & WSW 13) North Fork n/a 14) South Fork 15) Hunters Pass slides each enlarged

(Mellor 1997)

Cliff, SE

1971, 9/6 Whiteface, E & N cirques

12) Cliff slide

(Goodwin 1963)

16) Six Ski slides Thunderstorm. (Adirondack Record17) Enlarged/1 near Elizabethtown Post 1971) Wilmington Turn

1973, 6/23 (est.) Nippletop, W 18) Nippletop slide (aka Right to Life)

Three days of (Healy 1973) heavy rain

1979 South Meadow, n/a n/a n/a

(McMartin and Ingersoll 2001)

1983, 10/7

(Warren 2013)

Nye, NNW

19) Nye slide

Earthquake

1985 Santanoni, SW 20) Ermine Brook slide Hurricane Gloria

(McMartin and Ingersoll 2001)

1990, 6/16 Multiple High Peaks 10 slides including 21) Gothics True North 22) Finger slides 23) Colden (SE) 1990

(Silliman 1991)

10 inches of rain in one night

1991 Moose, NW 24) Moose Mtn. slide n/a

(Chilson, George, Tucker, and Wheeler 2003)

1993, Aug. (2nd week) Dix; N, NW 25) Six Slides

Two days of heavy rain

(McConaughy 1997)

1995, Oct.

Kilburn, WNW; Lower Wolfjaw, NW

26) Kilburn (aka Monument) slide 27) Bennies Root Canal slide

Cloudburst

(Manchester 2005)

1996, June

Peak 3149 near Snowy Mtn., E

28) Griffin Brook slide n/a * Not shown on Figure 1

(Chilson, George, Tucker, and Wheeler 2003)

1998, June

Saddleback

29) South Slide

Cloudburst

(Goodwin 2016)

1999, 9/16

Multiple High Peaks

12+ slides

Tropical Storm Floyd

(Peeks 1999)

2010

The Brothers, NE

2011, 6/3 Whiteface, NE/SE

30) Brothersâ&#x20AC;&#x2122; slide n/a Ski slides Storm (Lynch 2011) 31) #.5 32) #2B

2011, 8/27 Multiple High Peaks, At least 40 > 152.4 m All (500 ft long, undetermined number of smaller slides 2013, late June or early July

174

Dix, W

Tropical Storm Irene

33) Lobster Claw slide Rainstorms

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SLIDES ORIGINATING DURING TROPICAL STORM IRENE Tropical Storm Irene produced more slides than any storm in recorded history with at least 40 tracks measuring greater than 152.4 m (500 ft) in length including their runout. The longest (1.7 miles including the runout) lies on the northeastern aspect of Saddleback Mountain. The mountain’s Back in the Saddle slide was enlarged with a new tributary dubbed Catastrophic Chaos, a name that has gained popularity despite it being an enlargement of Back in the Saddle. The Northeast Shoulder slide on the east-southeastern aspect of Basin Mountain’s northeastern summit is one of the widest (nearly 500 ft near its base) in the 2011 set (see Figure 1). The northernmost significant outlier, Cooper Kill slide, avalanched on Wilmington Peak. The closest significant slide to a road is Cascade slide, the runout of which reaches Upper Cascade Lake between Keene and North Elba. Like the pre-existing slides, some of the 2011 creations are single track while others involve multiple tributaries converging downslope. Given the quantity of slides created it is unrealistic to describe each, but the following represent some of the most interesting created by the storm. Table 2 lists most of the significant Irene-related slides. Figure 4: Mark Lowell examining the debris at the base of Basin Mountain’s Northeast Shoulder slide. About two weeks after Tropical Storm Irene the smell of tannin and fresh wood was strong. Photo by author.

Basin Mountain: The 2011 damage to Basin Mountain in the heart of the Great Range, a combination of eight High Peaks and two lesser mountains, was vast. Prior storms have not been kind to this steep-flanked peak either. Tropical Storm Floyd added several scars to the mountain in 1999. Ten major and minor slides on multiple aspects were added to the collection in 2011. The most obvious of these lies on the east-southeastern aspect of the Basin’s northeastern shoulder – the Northeast Shoulder slide (44°7’18.4”N, 73°52’33.6”W). It is divided into four VOLUME 21

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distinct sections from bottom to top: the runout, a 152.4 m (500 ft) wide technical slab (enlarged on the eastern side by about 45.5 m [150 ft]), a low angle mid-section, and a steep, yet textured, track that narrows to a gully at the top. In contrast to some of the slides, this is one of the most remote with an approach of 13.7 km (8.5 mi) from the Garden trailhead in Keene Valley. The walk is through some of the most rugged terrain of the High Peaks. For the effort, one finds 1006 m (3300 ft) of slide and runout with over 442 m (1450 ft) of elevation gain. Cascade Mountain: Cascade slide (44°13’16”N, 73°51’59.1”W) on Cascade Mountain’s northwestern aspect was widely reported on since it is easily visible from Route 73 in Keene. This area is of particular interest to geologists due to its unique high-temperature contact metamorphic minerals formed when a large block of marble was incorporated into anorthositic magma (Valley and Essene 1980). The most obvious are large boulders of blue calcite and green diopside located in its runout. A minor “T” shaped slide, likely the remnants of the 1830 slide, adorned the mountain until 2011. This now constitutes the top of the most recent incarnation of the Cascade slide. Notable features of Cascade slide include a waterfall located a few minutes’ walk above the lakes, excellent exposure of minerals in the stream bed, and walls above the falls and a large inset dike (approximately 45.5 m [150 ft] long, 1.2 m [4 ft] wide, and 3 m [10 ft] deep). While nearly all slides contain dikes, the dimensions and characteristics of this one make it unique. Easy access with a challenging start makes this a popular venue for scramblers, ice climbers, and photographers. A walk of 152.4 m (500 ft) from the isthmus between the Cascade Lakes leads to the runout. The total distance to the top of the slide is 1207 m (3960 ft) with 427 m (1400 ft) of elevation gain. Mount Colden: The Trap Dike of Mt. Colden is an historic area used as the first known ascent route up Mt. Colden by Robert Clarke and Alexander Ralph in 1850 (Singer 2011). The dike was completely denuded of trees in 2011 by what was quickly named the Trap Dike slide (44°7’48.5”N, 73°57’44.2”W). It released on the northwestern aspect near the summit and stripped an ever-widening swathe of forest to the dike. A chock-stone the size of a small house sits in the Trap Dike and marks the bottom of the slide. On aerial photos, an apron of coarse debris can be seen extended outward from the lakeshore where the runout entered Cascade Lake. The approach to the slide base is just over 8 km (5 mi) from Adirondack Loj and involves climbing the Trap Dike to an elevation of 1173.5 m (3850 ft). The slide length is 548.5 m (1800 ft) with 259 m (850 ft) of elevation gain. Dix Mountain: Like Mt. Colden, Dix hosts dozens of slide tracks on multiple aspects. The Buttress slide (44°4’58.5”N, 73°48’0.8”W) on Dix Mountain’s western slope is particularly impressive because of its location and steep slope. The track avalanched

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down a cliff-riddled area of Hunters Pass, a narrow pass described by Alfred Billings Street in The Indian Pass as one of four gorges that are “peerless in majesty and awful beauty” (1869). Many slides can be easily climbed with appropriate caution and equipment, however, here the slope and features – cracks, corners, and twin roofs at its base—make it a technical slide rated 5.4 on the Yosemite Decimal System of rating. The approach to the base is just over 8.85 km (5.5 mi) from the Elk Lake trailhead. The slide length is 442 m (1450 ft) with 274 m (900 ft) of elevation gain. Lower Wolfjaw Mountain/Upper Wolfjaw Mountain: Various aspects of these neighboring High Peaks were affected by the storm. The watershed draining these slopes contributed to severe damage to the Johns Brook River Valley and along the Ausable River. Figure 5 shows the long slides on the Johns Brook side of Lower and Upper Wolfjaw Mountains. The bottom right track nearly destroyed a lean-to which was later moved to a location farther from the brook. Bennies Root Canal slide (44°9’30.5”N, 73°50’7.7”W) on Lower Wolfjaw Mountain’s northwestern aspect quickly became a classic venue for scramblers, skiers, and the occasional geologist (Chiarenzelli et al. 2015). Relatively easy access and a long length combined with a moderate slope contribute to its popularity. Low-angle slab dominates until the confluence of three tributaries (two from 1995). The terrain then steepens. The mid-section hosts an abundance of dikes, xenoliths, and other geologic features. A moderate walk of 3.86 km (2.4 mi) from Keene Valley’s Garden Trailhead leads to the bottom of the runout. The slide and runout length is 2.09 km (1.3 mi) with 564 m (1850 ft) of elevation gain. Khyber’s slide (44°9’8.3”N, 73°50’25.2”W) is an adjacent track that lies over a ridge to the southwest. It is similar in character on its lower portion but hosts two large “steps” or steep drops in the slide. Those looking for early season ice to climb are likely to find it here. The runout of Khyber’s slide crosses the Southside Trail a short distance to the southwest of Bennies Root Canal. The runout is not as clean as Bennies Root Canal, but a length of 2.25 km (1.4 mi) with approximately 457 m (1500 ft) of elevation gain makes it worth exploring. The neighboring Upper Wolfjaw Mountain hosts several enlarged slides on its northwestern ridge that share a common runout with Khyber’s slide. The uppermost track, the Skinny slide (44°8’35.1”N, 73°50’36.3”W), is an enlarged track of Tropical Storm Floyd in 1999. It has a longer approach and contains two features of note: a large dike dissecting the runout and a crevice about halfway up the slide proper. The crevice was created when a large piece of the face displaced and slid about a meter. Climbers can wriggle through the fissure and exit onto the slab above. Starting at the Garden Trailhead, an approach of 6.8 km (4.25 mi) leads to an 853 m (2800 ft) runout and slide track with 289.5 m (950 ft) of elevation gain.

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Figure 5: Photograph of Fall foliage and the long ribbons of Bennies Root Canal slide and Khyber’s slide in the foreground with Giant Mountain’s 1963 western cirque slides in the background. Photo by author.

Saddleback Mountain: Several slides, large and small, were created in close proximity along Orebed Brook on Saddleback Mountain and Gothics, its neighbor. The northeastern aspect Back in the Saddle slide (44°7’38.2”N, 73°52’23.2”W) had a large tributary dubbed Catastrophic Chaos (44°7’41.1”N, 73°52’22.1”W) intersect it high on the climber’s right. The tributary is almost 61 m (200 ft) wide at its widest point. It is the longest track in the Adirondacks including the slide proper and disrupted streambed. Nearby slides destroyed portions of the Orebed Trail, but this track runs adjacent with the trail and ends near the Orebed Lean-to. Moderately easy access

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and a long challenging slide with an interesting runout make it a popular destination for more experienced scramblers. The distance from the Garden Trailhead to the runout at the lean-to is 7 km (4.4 mi). The entire track is 2.7 km (1.7 mi) long with 527 m (1730 ft) of elevation gain. Wilmington Peak: Two steep headwalls of anorthosite were exposed on the northeastern flank of the peak in 2011. The slide then trends to the east. The Cooper Kill slide (44°26’1.6”N, 73°50’26.8”W) is notable as the northern outlier of the significant slides. Most of the runout is choked with rubble and other debris, but the headwall is a challenging climb with bailout options to the right. On a geologic note, it is also the only slide on which I have located a fossil —a gastropod in a small piece of displaced limestone, attesting to the power of ice to transport and deposit materials both laterally and, in this case, vertically. Those wanting to explore it only need only walk 2.8 km (1.75 mi) from the trailhead along Bonnieview Road in Wilmington. The slide and runout length is 1.6 km (1 mi) with 457 m (1500 ft) of elevation gain. Table 2: Select Tropical Storm Irene related slides. This table represents over 50 significant (>152.4 m [500 ft] in length) and minor slides. MOUNTAIN

SLIDE DETIALS

Algonquin Enlarged a slide in the Northeast Bowl (44°8’49.2”N, 73°58’53.7”W) and stripped Wright Brook’s streambed. Basin Created the Northeast Shoulder slide (44°7’18.4”N, 73°52’33.6”W) on ESE aspect of NE shoulder. Multiple new and enlarged slides in Chicken Coop slide array (44°7’34.6”N, 73°52’52.3”W) on the N aspect of Basin’s NE shoulder.

Created NW slide (44°7’21.0”N, 73°53’36.9”W) on Basin’s NW summit (Haas, 2016).

Created several small slides (44°6’59.2”N, 73°52’44.6”W) on Basin’s ridge S of the East Face. These slid into East Face run-out (44°7’5.5”N, 73°52’36.5”W) which was stripped to the Northeast Shoulder slide runout. Blake

Created three new slide tracks low on ESE aspect (44°4’45.8”N, 73°50’15.9”W).

Cascade Created Cascade slide (44°13’16”N, 73°51’59.1”W) on NW aspect from pre-existing “T” shaped slide. Colden

Created the Trap Dike slide (44°7’48.1”N, 73°57’44.2”W) on NW aspect near summit.

Trap Dike stripped of vegetation from 3,850’ in elevation to Avalanche Lake.

Enlarged Cruciflyer slide (44°8’11.4”N, 73°57’32.8”W) in NW gully enlarged to trail.

Created small slide (44°8’9.3”N, 73°57’38.2”W) on NW aspect of NE Shoulder.

Created Colden Cooler slide (44°7’51.8”N, 73°57’10.3”W) on NE flank of Colden’s NE Shoulder. Dix Added a tributary (44°4’51.6”N, 73°47’2.6”W) to the north of old Beckhorn slide on E aspect of mountain. Created Buttress slide (44°4’58.3”N, 73°47’58.6”W) on W aspect of Dix’ SW buttress. Enlarged Hunters Pass slide (44°5’3.6”N, 73°47’39.3”W) on W with two small tributaries along S edge.

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Giant Enlarged Putnam Brook slide (44°9’53.4”N, 73°44’8.4”W) below Giant’s NW shoulder. Enlarged Northeast slides (44°10’3.0”N, 73°43’8.9”W)—new tributary on W side and enlarged E tributary. Enlarged Tulip slide (44°9’23.7”N, 73°43’43.8”W) in WNW aspect in the W cirque). Enlarged Eagle slide drainage in W cirque (44°9’31.2”N, 73°43’31.3”W). Gothics

Created NW aspect slide in Orebed slide array (44°7’38.2”N, 73°51’55.0”W) E of Orebed Trail.

Lower Wolfjaw Enlarged Bennies Root Canal slide—new tributary descends N from summit; stripped runout NW to Johns Brook.

Created tributary Khyber’s slide; runs NW to Johns Brook.

Macomb

Enlarged multiple slides W/SW of summit (44°3’2.6”N, 73°47’6.9”W).

Marcy Created a small slide (44°6’39.9”N, 73°54’53.4”W) between the East Face slab and Grand Central slide. Saddleback

Created the Catastrophic Chaos tributary of the Back in the Saddle slide (44°7’39.5”N, 73°52’25.1”W).

Created a slide (44°7’40.2”N, 73°52’19.1”W) to the E of the Back in the Saddle slide.

Created several smaller slides (44°7’39.1”N, 73°52’13.2”W) between Back in the Saddle and the Orebed slides. Orebed slide (44°7’45.1”N, 73°52’4.1”W) on NNE aspect enlarged from a minor pre-existing exposure; intersects the Orebed Trail.

Created three slides (44°7’14.8”N, 73°52’8.8”W) on SE aspect of Saddleback’s S ridge.

Tabletop Created a slide on NNE aspect (44°9’17.8”N, 73°54’23.8”W) centered between Tabletop and Phelps Mountain. Old slide track had regrown.

Created a slide S of Howard Mountain on NE aspect of ridge (44°8’56.6”N, 73°53’21.2”W).

Upper Wolfjaw

Enlarged Skinny slide on NW ridge along its E side (44°8’35.5”N, 73°50’37”W).

Enlarged the Wide slide on NW ridge (44°8’48.1”N, 73°50’54.4”W). New slab was exposed at the bottom and along E and W sides of upper slab. Runout intersected the Range Trail and Southside Trail.

Created a N aspect slide (44°8’54.4”N, 73°50’40.3”W) between Skinny and Wide slides.

Created Beaver Brook slide (44°8’13.7”N, 73°50’38.5”W) on S aspect. Runout turns E. Wright Created new Angel slide (44°9’21.5”N, 73°58’1.9”W) on NE aspect adjacent to and NW of the 1999 Angel slides. Wilmington Peak

Created Cooper Kill slide (44°26’1.6”N, 73°50’26.8”W) on NE aspect. Runout turns E.

Created small slide (44°25’59.5”N, 73°50’27.0”W) adjacent to headwall of Cooper Kill slide.

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ACKNOWLEDGEMENTS

The author would like to Deb MacKenzie thank her insights and edits to this article as well as many others over the years; Don Mellor, Tony Goodwin, Adam Crofoot and Ron Konowitz for sharing their first-hand knowledge and insights regarding slide dates, names, and other facts; and Drew Haas for aerial photographs and associated information. J. Chiarenzelli reviewed this article and Lisa Grohn made Figure 1. L I T E R AT U R E C I T E D

Adirondack Record-Elizabethtown Post, The. 1971. “Mud Slides Play Havoc at Whiteface Mountain,” September 16, 63(36). Arnold, Doug. 2011. “Sawteeth Mountain,” in Heaven Up-h’isted-ness! The History of the Adirondack Forty-Sixers and the High Peaks of the Adirondacks. Cadyville: Adirondack Forty-Sixers, Inc., 478-481. Bogucki, D.J. 1977. “Debris slide hazards in the Adirondack province of New York State,” Environmental Geology, 12: 317-328. Brown, Phil. 2011. “The Big Rain,” Adirondack Explorer. Accessed December 2015 from http:// www.adirondackexplorer.org/stories/the-big-rain. Brown, Phil. 2011. “USGS Streamgages Under Threat,” Adirondack Almanack. Accessed January 2016 from http://www.adirondackalmanack.com/2011/11/phil-brown-usgsstreamgages-under-threat.html. Chiarenzelli, J., M. Lupulescu, S. Regan, D. Valentino, and D. Reed. 2015. “The Bennies Brook Slide: A window into the core of the Marcy Anorthosite: Field Trip A-1,” New York State Geological Association, Plattsburgh, New York, September 12-13, 27 pp. Chilson, Gary, Carl George, and Richard Tucker. 2003. An Adirondack Chronology. Adirondack Journal of Environmental Studies. Colvin, Verplanck. 1869. “A Huge Mountain Slide in the Adirondack Regions,” The New York Times, September 14. deWaard, D. 1970. “The anorthosite-charnockite suite of rocks of Roaring Brook Valley in the eastern Adirondacks (Marcy Massif),” American Mineralogist, 55: 2063-2075. Eagan, Daniel. 2011. “The Dix Range,” in Heaven Up-h’isted-ness! The History of the Adirondack Forty-Sixers and the High Peaks of the Adirondacks. Cadyville: Adirondack Forty-Sixers, Inc., 433-464. Eschner, Arthur. 1991. “Water and Landslides in the Adirondacks,” in T. Tefft (Ed.), Of the Summits, of the Forests, Morrisonville: The Adirondack Forty-Sixers, 179-181.

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Goodwin, Jim. 1963. “The Giant Slides,” Peeks, Fall/Winter 1963/1964, 6-7. Goodwin, Tony. Article. 2016. E-mail. Haas, Drew. Article. 2016. adkbcski@gmail.com. Hayes, El. 1928. “The Second Trail to Whiteface and the First From Lake Placid,” Lake Placid News, May 25, 7. Healy, Trudy. 1969. “New Route on Cliff,” Peeks, Fall 1969, VI(2): 15. Healy, Trudy. 1973. “Variety – Try a Slide,” Peeks, Fall 1973, X(2): 9. Joplin, Bill. 2013. “50 Years Ago: The 1963 Giant Mountain Landslide,” Adirondack Almanack. Accessed January 2016 from http://www.adirondackalmanack.com/2013/06/50-years-agothe-1963-giant-mountain-landslide.html. Kemp, J. 1921. “Geology of the Mount Marcy Quadrangle,” New York State Museum Bulletin, 229, 86 pp. Konowitz, Ron. 2011. “Big Slide,” in Heaven Up-h’isted-ness! The History of the Adirondack FortySixers and the High Peaks of the Adirondacks, Cadyville: Adirondack Forty-Sixers, Inc., 402-407. Lake Placid News. 1932. “Climbers Reach Landslide on Sentinel Peak,” August 19, 12. Lynch, Mike. 2011. “Slide at Whiteface Mountain expanded due to heavy rain,” Lake Placid News, June 6. Accessed January 2016 from http://www.lakeplacidnews.com/page/content. detail/id/503683/Slide-at-Whiteface-Mountain-expanded-due-to-heavy-rain.html. Manchester, Lee. 2005. “Through-Hiking the Old Iron Road,” Lake Placid News, December 2, 30. McConaughy, Stephanie. 1997. “Loving the North Slide on Dix,” Peeks, Fall/Winter 1997/1998, XXIV(2): 11-12, 29. McLelland, J.M., J.R. Chiarenzelli, and J. McLelland. 2016. “The intrusion breccia in the valley of Roaring Brook, Giant Mountain, Adirondack Highlands, New York: A modern interpretation,” Geosphere, February 5, 2016. DOI:10.1130/GES01260.1. McMartin, Barbara and Bill Ingersoll. 2001. Discover the Adirondack High Peaks, 140, 46-50. Canada Lakes: Lakeview Press. Mellor, Don. 1997. Climbing in the Adirondacks. Lake George: Adirondack Mountain Club. 402. Peeks. 1999. “Crews Dig Out High Peaks,” Fall/Winter 1999/2000, XXXVI(2): 25-26.

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Phelps, Orson Schofield. 1872. “Gleanings from Old Fields: Keene Flats-The Walton Slide,” Plattsburgh Republican, October 5. Accessed January 2016 from http://nyshistoricnewspapers. org/lccn/sn83031979/1872-10-05/ed-1/seq-3. Silliman, Keith. 1991. “Ascending Colden’s New Slide,” Adirondac, September/ October 1991, 18-19. Singer, Tim. 2011. “Mount Colden,” in Heaven Up-h’isted-ness! The History of the Adirondack Forty-Sixers and the High Peaks of the Adirondacks, Cadyville: Adirondack Forty-Sixers, Inc., 231-243. Stanne, Steve. 2012. “Perfect Storms,” New York State Conservationist, August, 8-13. Street, Alfred B. 1869. The Indian Pass. New York: Hurd & Houghton; Cambridge (Mass.): Riverside Press, 3. Tefft, Tim. 2011. “Whiteface Mountain,” in Heaven Up-h’isted-ness! The History of the Adirondack Forty-Sixers and the High Peaks of the Adirondacks, Cadyville: Adirondack Forty-Sixers, Inc., 539-557. Ticonderoga Sentinel. 1942. “Water Level of Lake is Raised by a Landslide,” October 1, 69(2). Valley, J.W., E.J. Essene. 1980. “Akermanite in the Cascade Slide xenolith and its significance for regional metamorphism in the Adirondacks,” Contributions to Mineralogy and Petrology, 74: 143-152. Warren, John. 2013. “Tornado Watch – Hazardous Weather Warning Issued,” Adirondack Almanack. Accessed December 2015 from http://www.adirondackalmanack.com/2013/10/ hazardous-weather-warning-adirondacks.html. Watson, Winslow. 1869. History of Essex County, 421(footnote). Albany: J. Munsell. West, Alfred. 1940. “The Slide on Wright,” High Spots, January, 62-64.

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GIANTâ&#x20AC;&#x2122;S WASHBOWL WITH THE FIRST FROSTING OF SNOW ON THE GREAT RANGE

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“ I am greatly indebted to the writings of previous geologists in this region, and the present paper is in part a ‘re-interpretation’ of the geology based on additional quantitative data and developed in the light of geologic thought at the present time.” Arthur Francis Buddington EXCERPT FROM HIS MEMOIR ADIRONDACK IGNEOUS ROCKS AND THEIR METAMORPHISM

1939

HANGING CLOUDS OVER THE UPPER GREAT RANGE

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