Aya Alygeochapter4

Aya Alygeochapter4 - Geology 100 Professor Ohan Chapter 4 1...

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Geology 100 Professor Ohan Chapter 4 1) Magma is the molten rock in the earth's crust. 2) Magma is the lava stored underground the volcano and lava is magma flowing down the volcano 3) The Earth's crust averages about 35 kilometers thick under the continents, but averages only some 7-10 kilometers beneath the oceans. The continental crust is composed primarily of sedimentary rocks resting on crystalline basement formed of a great variety of metamorphic and igneous rocks including granulite and granite. Oceanic crust is composed primarily of basalt and gabbro. Both continental and oceanic crust rest on peridotite of the mantle. 4) Rocks may melt in response to a decrease in pressure, to a change in composition such as an addition of water, to an increase in temperature, or to a combination of these processes. 5) Other mechanisms, such as melting from impact of a meteorite, are less important today, but impacts during accretion of the Earth led to extensive melting, and the outer several hundred kilometers of our early Earth probably was an ocean of magma. Impacts of large meteorites in last few hundred million years have been proposed as one mechanism responsible for the extensive basalt magmatism of several large igneous provinces. 6) Most magmas only entirely melt for small parts of their histories. More typically, they are mixes of melt and crystals, and sometimes also of gas bubbles. Melt, crystals, and bubbles usually have different densities, and so they can separate as magmas evolve. 7) As magma cools, minerals typically crystallize from the melt at different temperatures (fractional crystallization). As minerals crystallize, the composition of the residual melt typically changes. If crystals separate from melt, then the residual melt will differ in
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This note was uploaded on 02/05/2012 for the course GEOLOGY 101-101 taught by Professor Ohan during the Spring '11 term at CUNY City.

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Aya Alygeochapter4 - Geology 100 Professor Ohan Chapter 4 1...

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