is in the mantle. Hot rock moving toward the surface will have less pressure and will begin to melt. Flux melting can happen too. This is true for rocks when there is water added. Water will shift the melting curve so that wet mantle melts at lower temperatures compared to dry mantle. This means that all of these components – rock content, temperature, water presence, and pressure – all affect the melting ability of rocks in the mantle of the earth's crust. Rock partially melts on earth in a variety of situations. Plate tectonics contributes to this in different ways. Mantle plumes are areas where magma gets pushed nearer to the earth's surface. Wet mantle that subducts beneath the upper layers will melt as it gets sucked under the upper crust area. In these regions, partial melting of the silica components will occur as the rock sinks. Some components melt more so than others, so melting is uneven. . Hot spots are seen with volcanic islands, mid-oceanic ridge areas, subduction zones, and along continental rift zones. These are where the magma rises. Magma plumes often give rise to shield volcanoes full of lava. Silica will always melt earlier than basalt rock. At temperatures above 1300 degrees Celsius, all magma will be liquid. Then as it cools, the silica rock crystallizes earlier than the basalt, forcing the rest of the magma to be thicker in its consistency.
HOW MAGMA TURNS TO ROCK There is a sequence of reactions that happen when magma cools; these are called the Bowen reaction series. It is what explains the that magma can be liquid but will also have solid crystals in it. Olivine crystallizes first; any silica left over after this has crystallized mixes with the olivine to make pyroxene. Once pyroxene is formed, there will be a further reaction to create amphibole, and then biotite – all provided there is enough silica to finish the transformation. Pyroxene and plagioclase feldspar crystallize at the same time. Plagioclase has lots of calcium in it but as it cools, it will have more sodium in it. This is a continuous series, starting with calcium-rich plagioclase and becoming sodium-rich. This isn't what 93
