History of Rocks

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Associate Level Material

History of Rock Worksheet

Leah Bechtel
12/09/2012
SCI/245
Robert Dillon

Write a 500- to 750-word explanation regarding the role of plate tectonics in the origin of igneous rocks.

The role of plate tectonics in the origin of igneous rock is extremely important. Igneous rock is formed from magma that reaches the continental and oceanic crust or through hot spots that are around the world. There are three different places where igneous rocks can form; where the lithospheric plates pull apart at mid ocean ridges, where plates come together at seduction zones, and where continental crust is pushed together making the crust thicker and allowing it to heat to a melting point. The word igneous comes from the Latin word for fire, igneous rocks start off as a hot, fluid material which is usually erupted from the Earth’s surface as lava, or magma at shallow depths or deep depths. Magma is a mush like material that can carry a load of minerals, but people often think of lava and magma as a liquid like material of molten metals. The three types of igneous rocks are extrusive, intrusive and platonic rocks. Extrusive rocks are rocks that form and cool on the crust of the Earth whether it is on the continental crust or the oceanic crust. Extrusive rocks cool quickly, within a few seconds to months and they have invisible or very small grains; extrusive rocks have an aphanitic texture. Intrusive rocks are rocks that form within already existing rocks causing sills and dikes. Intrusive rocks cool slower than extrusive rocks, taking over thousands of years to cool completely and leaving them with small to medium sized grains. Plutonic rocks take over millions of years to cool and have large “pebble” size grains. These “pebbles” are often up to a meter across. Both intrusive and platonic rocks have a phaneritic texture. Hot spots are another way that magma is released onto the crust and when it is on the ocean floor can create new islands....
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