1.23.08 - Evidence for plate tectonics o Distribution of...

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1/23/08 Evidence for plate tectonics o Distribution of earthquakes and volcanoes This lecture o Large-scale motions of the continents (continental drift) o Rigidity of the plates Continents preserve shape during continental drift o Seafloor magnetic anomalies Next lecture Distribution of Earthquakes and Volcanoes o Earthquakes in the Atlantic define a very narrow boundary between the North American and Eurasian plates o Earthquakes and volcanoes in the Pacific outline the boundaries between the plates Principles of Plate Tectonics o The lithosphere is broken into a mosaic of moving plates – fragments of a spherical shell o Plates are rigid except near their boundaries, where relative motions between plates occur o New plate can be created at divergent boundaries and destroyed at convergent boundaries o Total plate area is conserved (No Earth Expansion!) Plate Boundaries o Divergent – moving apart Plates move apart, and the deeper mantle wells up and cools to
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Unformatted text preview: form new lithosphere Partial melting of the mantle creates magma, which forms oceanic crust Often marked by giant submarine mountain ranges on the ocean floor (mid-ocean ridges) Occasionally the divergent plate boundary will come above shore • Iceland is formed by the mid-Atlantic ridge o Convergent – moving together One plate slides beneath the other, and is recycled in the deep mantle. This is called a subduction zone Marked by deep trenches, and by chains of volcanoes, as in the Andes In continental collision, two continental plates hit each other; the one with the most density will be subdued and mountains will be formed on the less dense crust. e.g. the Himalayas o Transform – Pass horizontally Plates slide past each other horizontally, without any gain or loss of lithosphere. The boundary is a strike-slip fault e.g. the San Andreas Fault • offset rivers, highways, etc....
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  • Spring '08
  • Davis/Platt
  • Plate Tectonics, San Andreas Fault, divergent plate boundary, mid-Atlantic ridge o Convergent, Total plate area, plates Continents

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