(02)Tectonics&Cascades - GEOLOGY 20 - LECTURE 2...

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1 GEOLOGY 20 - LECTURE 2 PLATE TECTONICS & THE CASCADES (Ch. 1, 5 in Harden) Now that you know the geography of the Cascades and a bit about how volcanoes work, it’s time to address the WHY of the Cascades. Why do they form a linear pattern? Why are they active? Where’s the magma come from? These notes provide a very brief introduction to plate tectonics. We’ll get into greater detail as the course progresses. Plate Tectonics The global pattern of earthquake epicenters and volcano distribution exhibits linear trends, with earthquake epicenters and volcanoes commonly located along the edges of continents or strung out along linear trends down the middle of ocean basins. The locations of earthquakes and volcanoes coincide with the margins of plates - large, tabular sections of the Earth’s outer surface that are in constant motion. When they push together, mountains are built. When they pull apart, continents are split and ocean basins are created. - the surface of the Earth is in continual motion. New crust is being formed as we speak. Old crust is being destroyed. And all the surface of the planet is in constant slow motion. This process is called plate tectonics. Plate tectonics - the continual motion, creation, and destruction of parts of the planet’s active surface. Along with evolution, plate tectonics is the most important and encompassing theory in geology. It explains the uplift of mountain chains, the opening of ocean basins, the location of volcanoes, the occurrence of earthquakes, and predicts the location of mineral resources. plate ” refers to the shape of the moving sections of Earth’s outer surface. ~ 12 major plates plus several smaller plates; plates typically include both continents and parts of oceans (less commonly composed of just part of a continent or just part of an ocean basin). tectonics ” refers to large scale movement and deformation of Earth’s outer surface (crust plus upper mantle) How thick are tectonic plates? ~ 100-250 km (60-150 miles) To answer this question, we need to differentiate between layers in the Earth based on composition (i.e., crust, mantle, and core) and layers of the outer Earth based on strength (i.e., lithosphere and asthenosphere).
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2 layers of the Earth based on composition . . . Inner core
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This note was uploaded on 04/22/2008 for the course GEL 20 taught by Professor Osleger during the Spring '08 term at UC Davis.

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(02)Tectonics&Cascades - GEOLOGY 20 - LECTURE 2...

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