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Download 3-2 Earth`s Spreading Ocean Floor
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Theory of Plate Tectonics How do we know the plates exist? Earthquake and Volcano Zones Ocean floor features (Trenches and Mid-Oceanic ridges) Plate Boundary Features Lithospheric Plates 7 major Plates (continental crust, oceanic crust) The Earth is made up of a dozen or so major plates and several minor plates. Tectonic plates are constantly on the move. The fastest plate races along at 15 centimeters (6 inches) per year while the slowest plates crawl at less than 2.5 centimeters (1 inch) per year. Lithospheric Plate Cross Section How do we know the plates move? Evidence Supporting Continental Drift Movement of the Pacific Plate (Hawaiian island chain formed over a hotspot) How do the Plates Move? Explain this diagram: Sea Floor Spreading rift valley mid-ocean ridges newer less dense crust older more dense crust lithospheric plate magma asthenosphere Sea Floor Spreading A rift valley is volcanically active forming new oceanic crust on each side of the valley creating Mid-Ocean Ridges. The new crust pushes the older crust away from the mid-ocean ridge, moving the ocean floor & the continents Ex: Mid-Atlantic Ridge Evidence of Sea Floor Spreading Rock samples are younger closer to a mid-ocean ridge What Destroys Crust? Subduction Zones Occurs when oceanic crust collides with oceanic or continental crust The older, more dense, oceanic crust plunges back into the mantle at a deep ocean trench. Forms deep ocean trenches & volcanic mountains or island arcs. Trenches of the World Plate Collisions Oceanic Continental Subduction Oceanic Oceanic Subduction Continental– Continental (No Subduction) Convergent Margins: India-Asia Collision II Three Plate Boundaries Divergent – plates move apart; sea floor spreading Convergent – Plates collide together; subduction Transform (strike-slip) – Plates slide past each other; San Andreas fault Transform Boundary: San Andreas Fault Motion at Plate Boundaries Plate Boundaries What Causes the Plates to Move? Convection Currents in mantle Ridge Push Slab Pull Lava Lamp Convection Convection and Tectonics
