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Chapter 18 Plate Tectonics: Notes

Chapter 18 Plate Tectonics: Notes - Chapter 18 Plate...

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Chapter 18 Plate Tectonics: Notes 1. asthenosphere – low velocity zone that is hot, elastic semiliquid layer that extends around the entire earth. Named after Greek word for “weak shell”. Seismic waves undergo a sharp decrease in velocity at this level. 2. convergent boundaries – occur between two plates moving toward each other. Creation of new crust at a divergent boundary means that old crust must be destroyed somewhere else at the same rate or else the earth would continue to expand its diameter. The old crust is destroyed by returning to the asthenosphere at convergent boundaries. Produce related characterisitic geologic features depending on the nature of the materials in the plates. Three general possibilities (1) convergining continental and oceanic plates. This produces an oceanic plates of denser basaltic material and is sub ducted beneath the less dense granite type continental plate. Or (2) ocean-ocean plate convergence produces different geologic features such as island arcs. Curving chains of volcanic islands that occur over the belt of a deep-seated earthquake area. Finally (3) continent-continent plate convergence, subduction does not occur as the less dense, granite-type materials tend to resist subduction. The colliding plates pile up into a deformed and thicker crust of the lighter material. This collision produces the thick, elevated crust know as the Tibetan Plateau and the Himalayan Mountains. 3. Core – center part of the earth. All evidence gained by use of seismological data, nature of mereorites, and geological data. 4. Crust – a thin skin that covers the entire earth. Exists below the oceans as well as making up the continents. Oceanic crust is much thinner than continental crust. Seismic waves move through the
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