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Plates_Lecture - Finish Chapter 22 Plate Tectonics II Next...

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Plates lithosphere and asthenosphere Divergent boundaries (plates pulling apart) East African Rift Convergent boundaries (plates colliding) ocean-ocean ocean-continent continent-continent Transform boundaries (plates slipping sideways) Hot spots Mantle convection Finish Chapter 22: Plate Tectonics II Next lecture: Chapter 23
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The Arabian Peninsula, Horn of Africa, Gulf of Aden, and lower part of the Red Sea as seen from a satellite (note the antenna in the lower left).
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A “hotspot,” a region of unusually warm mantle material under Africa formed a blister that continued to elevate and expand, and then split along a three-cornered tear (rift zones). Two of these developed into seaways (Red Sea, Gulf of Aden) as the third “failed” arm became the rift valleys of East Africa.
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http://geology.com/articles/east-africa-rift.shtml Relative motions for the three components of the East African Rift system. Flood basalts are thought to be a common outcome of hot- spot interactions with continental crust.
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http://geology.com/articles/east-africa-rift.shtml Doming and rifting through Africa suggest continued hot-spot activity, and that the “failure” of the third arm may be only temporary.
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The rifting process in Africa as seen in cross section. First, the crust is elevated, stretched, and thinned (A). Later, lakes occupy fault- bounded rift valleys (B). Finally the continental crust is completely severed apart, and new ocean crust (orange) appears (C) that continues to widen (D).
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Plates lithosphere and asthenosphere Divergent boundaries (plates pulling apart) East African Rift Convergent boundaries (plates colliding) ocean-ocean ocean-continent continent-continent Transform boundaries (plates slipping sideways) Hot spots Mantle convection Finish Chapter 22: Plate Tectonics II Next lecture: Chapter 23
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The worldwide ocean trench system chiefly rims the Pacific Ocean.
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Now let’s interpret processes in the Tonga Trench in the light of plate-tectonic theory.
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A reminder: earthquakes associated with the Tonga Trench occur at the trench floor, and to a depth of as much as 650 kilometers, well within the mantle.
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Moreover, the earthquake foci are arrayed along a dipping plane as seen here in cross section. Most of them are “deep focus” earthquakes.
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Now the plate tectonic interpretation.
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