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Chapter 10.2 Plate Tectonics Putting It All Together ... Plate Tectonics Plate Tectonics –the theory that combines elements of continental drift and seafloor spreading into a more far-reaching explanation that not only explains that continents and ocean basins move, but explains how they move. http://www.youtube.com/watch?v=6CsTTm vX6mc http://www.youtube.com/watch?v=6CsTTmvX6mc The Lithosphere and the Asthenosphere Lithosphere – the Earth’s crust (both oceanic and continental) combined with the rigid, upper mantle that forms the outer shell of the Earth. Asthenosphere – the “plastic” (i.e. It flows.), lowerupper mantle directly underneath the lithosphere. The asthenosphere is plastic because of the pressure on it from the lithosphere above. The less dense, lithospheric plates, including the oceanic and continental crust, “float” on the more dense, “plastic” asthenosphere directly below. Earth’s Crust … Its Not All Created Equally!!! Oceanic Crust – the Earth’s crust under the oceans that makes up the ocean basins (ranges from 5 to 10 km thick). Continental Crust – the Earth’s crust that makes up the continental landmasses (ranges from 15 to 80 km thick). Ocean crust is made of a more dense material than continental crust. Plate Tectonics According to Plate Tectonics, the Earth’s crust is broken up into a series of at least 15 constantly moving plates that interact at their boundaries in order to form and constantly reshape the Earth’s surface. How do we know that plates are there? Two Major Surface Features That Show Border Tectonic Plates are: 1. Mountain Ranges 2. Deep Trenches When there is movement along a plate boundary, an earthquake may occur (http://earthquake.usgs.gov/eqcenter/index.php). A well-known feature that may help identify a plate boundary is a volcano (ex. the volcanoes of the Pacific Ring of Fire). Plate Tectonic Action … Types of Lithospheric Plate Boundaries Divergent Boundaries - two plates are moving away from each other. Convergent Boundaries - two plates coming together and colliding. Transform Fault Boundaries - two plates sliding past one another and grinding. http://www.thetech.org/exhibits_events/online/quakes/plates/divergent.html Divergent Boundaries At these divergent boundaries, magma upwells between the two plates as they diverge. Most of these plates are ocean ridges (ex. a MidOcean Ridge). Click below to learn more about divergent boundaries. file://localhost/Volumes/Faculty_Groups/Science/Earth Science/MU Earthquake Wkshp/EarthScope CD/3_Animations & Movies/Plate Interaction_Converge Diverge Transform/Plates Diverge_Extension/DivergentPlateMargin.mov Convergent Boundaries … Type 1 The first type of convergent boundary is a subduction zone. At a subduction zone, a denser, ocean plate is forced beneath a less dense, continental plate. As the ocean plate moves down towards the mantle, it melts, causing an upwelling of magma. This upwelling of magma produces volcanic mountains (ex. the Andes Mountains in South America). file://localhost/ Volumes/Facult y_Groups/Scie nce/Earth Science/MU Earthquake Wkshp/EarthSc ope CD/3_Animatio ns & Movies/Plate Interaction_Co nverge Diverge Transform/Plat es Converge_Co mpression/Sub duction&Volcan oes_Narrated. mov file://localhost/Vol umes/Faculty_Gr oups/Science/Eart h Science/MU Earthquake Wkshp/EarthScop e CD/3_Animations & Movies/Plate Interaction_Conve rge Diverge Transform/Plates Converge_Compr ession/Subductio n&VolcanoesUCSB.mov Click below to learn more about convergent boundaries. Convergent Boundaries … Type 2 The second type of convergent plate boundary occurs when two continental plates converge. Since the two plates have similar densities, rather than one going under the other, the crumple, fold, and uplift forming a mountain range (ex. the Himalayas in Asia). file://localhost/Volumes/Faculty_Groups/Science/Earth Science/MU Earthquake Wkshp/EarthScope CD/3_Animations & Movies/Plate Interaction_Converge Diverge Transform/Plates Converge_Compression/SubductionW:ContCollision_UCSB.mov Convergent Boundaries … Type 3 The third type of convergent plate boundary occurs when two oceanic plates converge. One plate is subducted under the other, forming a deep trench. The subducted plate melts and an island chain, called an island arc, forms (ex. the Japan in Asia). Transform Fault Boundaries At these transform fault boundaries, rough spots may cause sudden spurts in tectonic activity (i.e. earthquakes) followed by relatively no activity (ex. the San Andreas Fault in San Francisco, CA). How Plates Move … Convection Cells Currently, scientists believe that plates move because of convection currents that occur deep within the Earth. Like a pot of boiling water bubbling on a stove, magma warms, becomes less dense, and upwells, and is in turn replaced by cooler, more dense, sinking material. This movement, called a convection cell, appears to be greatest at plate boundaries and may explain the movements of plates at those locations. Cold fluid Warm fluid How Plates Move … Ridge Push/Slab Pull Ridge push - as the cooling lithosphere sinks at a ridge, the warmer asthenosphere below pushes on the under side of the plate as it flows out and away from the ridge. Slab Pull - as the leading edge of a subducting lithospheric plate is pulled downward, it pulls the rest of the plate down with it. Ridge push Slab Pull The End All images came from Google and are for educational purposes only!!!