_07_Plutonism - GEL 1 Lecture 7 Magma and Igneous Rocks Up...

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GEL 1: Lecture 7 Magma and Igneous Rocks: Up from the Inferno Igneous Rocks An igneous rock forms from the progressive cooling of molten rock (aka crystallization from a melt). It can occur either slowly beneath the surface associated with a magma chamber , or it can occur rapidly on the surface of the land or seafloor as lava ‘freezes’ to rock. (see the Minerals notes on ‘crystallization from a melt’) When magma rises up into the lithosphere, it can do two things: it can erupt on the surface from a volcano or it can solidify at some depth beneath the surface. - igneous rock that solidifies beneath the surface is called intrusive igneous rock and the process is called plutonism . - igneous rock that solidifies on the surface of the land or along the seafloor is called extrusive igneous rock and the process is called volcanism (which we'll discuss separately). The earliest rocks on Earth were igneous. The early Earth was so hot from 'heat of formation' generated by countless collisions with space debris that its surface was likely molten. - as Earth cooled with time, parts of this magma ocean began to solidify into thin crusts (the first 'continents'). As the Earth cooled even more, the entire mantle 'froze', forming a thick, semi-plastic shell around the metallic core. Igneous rocks are the most abundant on Earth, comprising all the mantle, all of the oceanic crust (remember that all ocean crust forms at mid-ocean ridges), and much of the continental crust. - even though volcanism is a very common phenomenon on Earth's surface, the vast majority of igneous rocks form beneath the surface by plutonism. Where and how is magma produced? Magma forms in the uppermost asthenosphere and throughout the lithosphere and crust where pressures from overlying rock are not as great as deeper in the Earth. - rock in the asthenosphere and deeper mantle is solid. It may be hot and mobile and migrate slowly as a thick 'plastic', but it is nevertheless a solid rock. - only when certain conditions are met does this solid rock melt into magma
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This note was uploaded on 11/22/2010 for the course GEL 1 taught by Professor Barfod during the Spring '08 term at UC Davis.

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_07_Plutonism - GEL 1 Lecture 7 Magma and Igneous Rocks Up...

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