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7-3: Theory of Plate Tectonics Lithospheric tectonic plates float on asthenosphere 3 types of plate boundaries (fill in Tectonic Plate Boundaries sheet) • Transform • Divergent • Convergent Animation of plate boundaries (website) Transform • slide past each other horizontally (opposite direction) ex: San Andreas fault (CA) may produce earthquakes San Andreas Fault (website) California (2 plates) North American Plate Pacific Plate San Andres Fault • Divergent—plates separate ocean-ocean=sea-floor spreading (mid-ocean ridge) continent-continent=rift valley East African Rift (from Ethiopia to Kenya)– divergent boundary • Convergent—collide oceanic-oceanic plates creates island arch (volcanic) ……animation (website) ocean-continent plates (denser ocean plate moves DOWN and continental plate folds upward) creates trench (at subduction zone) and volcanoes inland ……animation (website) continent-continent plates creates mountains …..animation (website) Aleutian Islands (between Alaska and Russia) formed as 2 oceanic plates collided Mt. St. Helens (Washington state) Created by ocean-continent collision Andes Mountain (oceancontinent convergent boundary) Himalayas (Asia) formed as 2 continents collided (still growing) Other Websites http://www.pbs.org/wgbh/aso/t ryit/tectonics/shockwave.html (what happens at the plate boundaries!) Summary of Plate Tectonics (Enchanted Learning) plate tectonics online tutorial Question Sea-floor spreading occurs at which of the following types of tectonic plates? • a. • b. • c. • d. transform convergent divergent strike-slip Possible causes of tectonic motion — convection currents (website) in asthenosphere tracking plate motion with GPS— plates move only a few cm per year What features of Earth are produced by the movement of lithospheric plates? >>mountains, volcanoes, volcanic islands, rift valleys 1. Earthquakes are MOST LIKELY to occur at the borders of _________. >>>>>lithospheric plates 2. The collision of two continental plates can produce _____________. >>>>>>a mountain range (not a single mountain) 3. Plate tectonics describes movements MAINLY in ___________. >>>>Earth crust (or lithosphere) 4. Which ocean was produced by sea-floor spreading between Africa and South America? >>Atlantic 5. As distance increases from a mid-ocean ridge, the rocks grow older or younger? >>>>>older 6. The “ring of fire” helps scientists predict areas where ___________ are likely to occur. >>earthquakes and volcanoes 7. Volcanoes can be produced by the collisions of ____& _______ plates. >>oceanic and oceanic continental and oceanic OR More questions A convection current of magma is made up of a. a rising more dense liquid and a sinking less dense liquid. b. a rising less dense liquid and sinking more dense liquid. c. liquids of the same density. d. solids of different densities. How do mid-ocean ridges support both the idea of continental drift and the theory of plate tectonics? • a. Oceanic lithosphere is destroyed at mid-ocean ridges. • b. New crust forms at mid-ocean ridges. • c. Tectonic plates collide at mid-ocean ridges. • d. The crust at mid-ocean ridges is old oceanic lithosphere.