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EPS 201 PLATE TECTONICS

EPS 201 PLATE TECTONICS - EPS 201 17 FEB 2009 Plate...

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EPS 201: 17 – FEB – 2009 Plate Tectonics 1. What are plates? 2. What are their boundaries? 3. Divergent plate boundaries. Dr. Elrick has chosen today to give us an illustration regarding convection in a boiling pot of milk. In the example, she is showing that the milk at the bottom of the pot will get hot first, become less dense, and rise to the top. At the top, it will cool, and move to the sides, and will begin to sink with its new higher density, while other parts of the milk are rising with heat. So – the plate in plate tectonics is the upper 60 km or so of the crust. The plate is in the – it is strong, rigid and relatively cool. It floats on top of the – in contrast to the lithosphere, the asthenosphere is weak, and partially melted. So, the asthenosphere, while “partially molten” is actually mostly (85%) crystals and the rest is molten rock. The lithosphere is composed of a crust, which can be thick material (more granitic in composition), has a lot of the light minerals such as quartz and feldspar. This is lithosphere asthenosphere
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what the continental crust is mostly made up of. The continental crust is lighter in density, and thicker. It floats on top of the upper mantle. The oceanic crust is completely different, being more mafic in composition, and it has a higher density due to its composition. Both the continental and the oceanic crusts are floating on top of the lithosphere, which is highly composed of , which is a higher density rock. As you go deeper into the upper mantle, the rock gets warmer getting up to about 1300° C, where the rock begins to get more molten and gives the lithosphere the capability to slide over the top of it. So, the plate is about 100 km thick – has oceanic crust at the top or has continental crust at the top. The question as to how the plates move around is answered by the convection process of the molten rock in the mantle, which has a constant movement similar to the movement of liquid in a boiling pot of water. peridotite
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Seismic waves are used to determine the depth of the crust and plates, being that the pressure generated by seismic waves experiences more resistance in liquid than in solid pathways, allowing investigators to determine the depth of the solid level. On average the ocean floor sits 4 km below sea level. She’d like us to understand that from the surface of the earth at any point to the point of low velocity (boundary of the asthenosphere/lithosphere) should weigh the same, regardless of the thickness of the crust.
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