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4.2 The Theory of Plate Tectonics Tectonics – (Greek) meaning “construction” Tectonics: The study of the formation of features in the earth’s crust Open textbook to p. 72 Two types of crust: • Oceanic crust • Continental crust Lithosphere & Asthenosphere Lithosphere – made up of the crust and the rigid upper mantle The lithosphere is broken into separate plates that ride on the denser asthenosphere. Asthenosphere – layer of plastic rock; a solid rock that slowly flows(like putty) when under pressure. Plate Boundaries Divergent boundaries – where plates move away from each other Plate Boundaries Convergent boundaries – where plates collide (3 types) 1. Ocean & Continent – forms a subduction zone; usually forms an ocean trench and mountains on land Plate Boundaries Convergent boundaries – where plates collide 2. Two Continental plates – neither plate is subducted, so both are crumpled and uplifted Plate Boundaries Convergent boundaries – where plates collide 3. Ocean & Ocean – forms deep ocean trench when one plate is subducted; subducted plate melts and forms volcanic chain (Island Arc) Plate Boundaries Transform fault boundaries – forms where two plates are grinding past each other. Can you think of an example? San Andreas Fault Causes of Plate Motion Convection Currents – cycle of warm matter rising and cool matter sinking Theory of Suspect Terranes Continents are a patchwork of terranes, each with its own distinct geologic history. 3 identifying characteristics: 1. Terrane contains rock and fossils that differ from the rocks and fossils of neighboring terranes. 2. There are major faults at the boundaries of a terrane. 3. The magnetic properties of a terrane do not match those of neighboring terranes See Figure 4-9 on p. 77