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Plate Tectonics What is Plate Tectonics? • The Earth’s crust and upper mantle are broken into sections called plates. • Plates move around on top of the mantle like rafts. The Crust • This is where we live! • The Earth’s crust is made of: Continental Crust Oceanic Crust - thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old - thin (~7 km) - dense (sinks under continental crust) - young World Plates What are tectonic plates made of? • Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle. What lies beneath the tectonic plates? • Below the lithosphere (which makes up the tectonic plates) is the asthenosphere. Plate Movement • “Plates” of lithosphere are moved around by the underlying mantle convection currents. – Also, gravity pulls harder on the more dense oceanic plates. Questions... • What causes plates to move? • How is a convection current formed? Questions... • What is the theory of plate tectonics? • What is the lithosphere? • What is the asthenosphere? • What is the connection between the two? • What are the two types of plates? Plate Boundaries Three types of plate boundary • Divergent • Convergent • Transform Divergent Boundaries • Seafloor Spreading – As plates move apart new material is erupted to fill the gap Age of Oceanic Crust Courtesy of www.ngdc.noaa.gov Iceland: An example of continental rifting • Iceland has a divergent plate boundary running through its middle Convergent Boundaries • Two plate that are colliding • There are three styles of convergent plate boundaries – Continent-continent collision – Continent-oceanic crust collision – Ocean-ocean collision 1. Continent-Continent Collision • Forms mountains, e.g. European Alps, Himalayas Himalayas 2. Continent-Oceanic Collision • Called SUBDUCTION Subduction • Oceanic lithosphere subducts underneath the continental lithosphere • Oceanic lithosphere heats and dehydrates as it subsides • The melt rises forming volcanism • E.g. The Andes 3. Ocean-Ocean Collision • When two oceanic plates collide, one runs over the other causing it to sink into the mantle forming a subduction zone. • The subducting plate is bent downward to form a very deep depression in the ocean floor called a deep-sea trench. • The deepest parts of the ocean are found along trenches. – The Mariana Trench is 11 km deep! Transform Boundaries • Where plates slide past each other Above: View of the San Andreas transform fault Questions... • What are the three types of boundaries? • What direction do plates go for each? • Which boundary has a subduction zone…what occurs at a subduction zone? Side Effects • Earthquakes and volcanoes transfer energy from Earth’s interior to the surface. • Earthquakes – mechanical energy • Volcanoes – thermal and mechanical energy