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Plate Tectonics Tectonic Plates of the Earth Plate tectonics Today we will explore…. Different type of Plates Different types of Plate Boundary (where the two plates are touching) Different directions of plate movement Results of what is created by all three of these items Plate tectonics Types of plates….(2) Oceanic Plate and Continental Plate mainly defined along the boundary where the two plates touch, for example…while most plates are comprised of both continental and oceanic crust the giant Pacific Plate is almost entirely oceanic, and the tiny Turkish-Aegean Plate is entirely land. Plate Boundary…..(3) Ocean to Ocean Ocean to Continental Continental to Continental Plate tectonics Direction of Movement (3) Plates are either……. Convergent Colliding….there are 2 different types of convergent Divergent Pulling apart (spreading) Transgressional/Transformational Sliding past one another Plate tectonics What happens when plates move, collide, etc Mountains, Trenches, Volcanoes, Islands, rift valley, earthquakes, etc, etc, etc Plate tectonics Convergent Movement Two plates colliding….one usually goes down. Subduction –usually when an ocean plate collides with a continental plate the Ocean plate “subducts” under the continental plate. Over-riding –usually when a continental plate collides with another continental plate. One of the plates usually subducts, but the other plate will also Over-ride the other plate. Plate tectonics Convergent Movement Convergent plate boundaries have the following characteristics: 1. plate motion is toward plate boundary, 2. oceanic lithosphere sinks back into Earth and is recycled, 3. the volcanic arc is region of highly explosive volcanoes, like Mt. St. Helens and Mt. Rainer in Washington, 4. The plate boundary is marked on the seafloor by a deep-sea trench, or just trench, the deepest areas of the ocean, 5. These types of plate boundaries have the strongest earthquakes and most explosive volcanic eruptions! Ocean-to-continent subduction - An oceanic plate is subducted beneath a continental plate, forming a trench adjacent to a continent, and volcanic mountains along the edge of the continent. Example: Peru-Chile Trench adjacent to the western coast of South America and the Andes Mountains. Note that the volcanic rocks in this setting tend to be andesite (named for Andes Mountains) - coming from a mixture of basaltic and granitic magmas. Ocean-to-ocean subduction - An oceanic plate is subducted beneath another oceanic plate, forming a deep-sea trench, with an associated basaltic volcanic island arc. Examples: Marianas Trench adjacent to Mariana Islands, Aleutian Trench adjacent to Aleutian Islands, Java Trench adjacent to Java, Sumatra, and Sunda Islands in the Indonesian region. A second type of convergent plate boundary involves the sinking of oceanic lithosphere beneath another plate of oceanic lithosphere -- these regions have the very deepest trenches along the seafloor and a line of volcanic islands, called an island arc. Once again these regions have explosive volcanoes. Continental collisions (convergent movement also called Over-riding) form mountain belts with folded sedimentary rocks, and a central area of metamorphic rocks. and granitic igneous intrusions. Examples: Himalaya Mountains, Ural Mountains, Appalachian Mountains * Non-volcanic Continental to Continental Convergent Converging 3 types A. Oceanic-Continental volcanic ranges e.g. Andes B. Oceanic-Oceanic volcanic island arcs e.g. Japan, Aleutian islands C. Continental-Continental mountain ranges e.g. Alps, Himalayas Plate tectonics Divergent Movement Two plates pulling apart or spreading….they are “diverging” from each other. Most common when two oceanic plates are diverging, but can occur on land between two continental plates Divergent/Spreading boundaries When a divergent boundary occurs beneath oceanic lithosphere, the rising convection current below lifts the lithosphere producing a mid-ocean ridge. Extensional forces stretch the lithosphere and produce a deep fissure Examples - Mid-Atlantic ridge (two ocean plates), Great Rift Valley (two continental plates) Major Divergent Boundry Animation Plate tectonics Transformational Movement Two plates sliding past one another….usually involves one plate doing most of the moving, the other being stationary Ocean to continental plate - San Andreas Ocean and Ocean – Steps on the Mid Atlantic Ridge Transform boundaries, in many places, form steps in the mid-ocean ridges. These boundaries mark regions where one oceanic plate slips horizontally by another oceanic plate -- lithosphere is neither created or recycled, but it is conserved. Plate motion is parallel to the plate boundary and can result in very large earthquakes. With a few exceptions, transform plate boundaries do not exhibit volcanoes, but can right along the boundary (Calif does have volcanoes but eruptions are very rare) Steps on Mid Atlantic Ridge Ocean and Continental transformation Transform boundaries • associated w/ major seismic activity How is it all connected? Earthquakes, faults, volcanoes, etc We will do an activity that allows you to make connections with all types of movements and what the produce. Plate tectonics in the future: 50 my • • • • • Australia will straddle the equator E. Africa will form new continent Mediterranean will close off Atlantic Ocean will grow Pacific Ocean will shrink