Chapter 9 _ Continental Tectonics and Mountain Chains

Chapter 9 _ Continental Tectonics and Mountain Chains -...

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Chapter 9 – Continental Tectonics and Mountain Chains By: Dionne Castillo Continental Crust undergoes changes along all three kinds of plate boundaries: 1. Spreading zones: 2. Subduction zones: 3. Transform or strike-slip faults: a. An example is The San Andreas fault in California. Continental crust is about 5 times thicker than oceanic crust. A rift may begin to fracture a continent and then fail to complete the break, leaving telltale scars of its activity. The Rifting of Continents A rift is a place where the Earth’s crust and lithosphere are being pulled apart. Hot Spots give rise to three-armed rifts When rifts develop, they often begin as three-armed grabens at plate boundaries known as triple junction. The continental crust of the locations of three-armed grabens is frequently a dome. This elevation represents the development of a hot spot. More than one kind of plate boundary can meet at a triple junction: it may be a spreading zone, subduction zone or transform fault. When a large continent breaks apart, the jagged line along which it divides often represents a composite structure formed from arms of several three-armed rifts. A three-arm rift usually contributes two of its arms to the composite rift, while the third arm becomes a failed-rift- a plate tectonic dead end. Rift valleys form when continental breakup begins When a spreading zone first encounters continental crust its extension along a rift tends to break the thick continental crust into a complex band of fault blocks. These valleys, also known as fault block basin create a rugged landscape that is subject to rapid erosion. If rifting continues long enough, a rift valley becomes so wide and so extended that it opens
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Chapter 9 _ Continental Tectonics and Mountain Chains -...

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