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Plate Tectonics What do these things have in common? What could those things possibly have to do with boiling pasta?? Convec:on currents Plate Movement • “Plates” of lithosphere are moved around by the underlying hot mantle convection cells Convec:on Currents • Hot magma in the Earth moves toward the surface, cools, then sinks again. • Creates convection currents beneath the plates that cause the plates to move. Three types of plate boundary • Divergent • Convergent • Transform Divergent Boundaries • Spreading ridges – As plates move apart new material is erupted to fill the gap Oceanic/Oceanic Divergent ß à • Sea floor spreading – ocean grows • Forms Mid-Ocean Ridges • Example – • Mid Atlantic Ridge • Forms a trench in the middle Age of Oceanic Crust Mid-Atlantic Ridge Red – youngest crust Blue – oldest crust Gray- land Courtesy of www.ngdc.noaa.gov Continental/Continental Divergent ß à • Africa’s Great Rift Valley • Can you tell where the continent is separating? Iceland: An example of continental rifting • Iceland has a divergent plate boundary running through its middle Convergent Boundaries • There are three types of convergent plate boundaries – Continental-oceanic crust collision – Oceanic-oceanic crust collision – Continental-continental crust collision Continent-Oceanic Crust Collision • Called SUBDUCTION Subduction • Oceanic lithosphere subducts underneath the continental lithosphere • Oceanic lithosphere heats and melts into the magma as it sinks • The pressure causes magma to press up through the boundary, creating volcanic mountains • E.g. The Andes Mountains The Andes Mountains • The longest mountain range in the world. • In 7 countries in South America Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, & Argentina. Oceanic-Oceanic Plate Collision • When two oceanic plates collide, one runs over the other which causes 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 trench. • The worlds deepest parts of the ocean are found along trenches. Oceanic-Oceanic Plate Collision • The pressure causes volcanoes to rise up. When these volcanoes stick out of the water, they form what is called an island arc, or a string of volcanic islands Aleutian Islands Alaska, USA Continental-Continental Collision • Forms folded mountains, • e.g. Himalaya Mountains Himalayas Transform Boundaries • • Where plates slide past each other (horizontally) The friction causes earthquakes Above: View of the San Andreas transform fault, California Plate Tectonics Summary • The Earth is made up of 3 main layers (core, mantle, crust). • On the surface of the Earth are tectonic plates that slowly move around the globe • Plates are made of crust and upper mantle (lithosphere) and float on the asthenosphere • There are 2 types of plates • There are 3 types of plate boundaries • Volcanoes and Earthquakes are closely linked to the margins of the tectonic plates Who figures all this out?