Lecture10 platetectonics

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Lecture10 platetectonics

  1. 1. Plate Tectonics Tectonic Plates of the Earth
  2. 2. How can we explain the rock cycle? <ul><li>Need to identify mechanisms by which rocks are </li></ul><ul><ul><li>Heated and melted </li></ul></ul><ul><ul><li>Buried and metamorphosed </li></ul></ul><ul><ul><li>Pushed up into mountains to be eroded </li></ul></ul>
  3. 3. Earth as a jigsaw puzzle <ul><li>Matching continental edges: recognized for centuries </li></ul><ul><li>Pangaea: supercontinent proposed by Wegener (1912) </li></ul>
  4. 4. Wegener’s contribution <ul><li>continental drift </li></ul><ul><li>= pattern of moving continents </li></ul>
  5. 5. Theory of fixed continents <ul><li>Traditional assumption: continents & ocean basins fixed in position </li></ul><ul><li>Problems </li></ul><ul><li>Matching continent edges </li></ul><ul><li>Matching fossils among continents </li></ul><ul><li>Matching geology among continents </li></ul>
  6. 6. Evidence against fixed continents Matching edges Matching geology
  7. 7. Bathymetry of the ocean floor continental shelf abyssal plain trench mid ocean ridge
  8. 8. Thickness of the Sediment x 550 m x 102 m x 18 m x 112 m x 430 m 35 m x
  9. 9. The Driving Mechanism
  10. 10. Paleomagnetism
  11. 11. Radiometric dating Red = younger, green = older
  12. 12. Plate tectonics <ul><li>= process for continental drift </li></ul><ul><li>Thermal convection system within Earth </li></ul><ul><ul><li>1. Making crust </li></ul></ul><ul><ul><li>2. Destroying crust </li></ul></ul><ul><ul><li>Explains the rock cycle! </li></ul></ul>
  13. 13. Making crust <ul><li>magma rises up from mantle, spreads out, & cools </li></ul><ul><li>occurs at spreading boundaries (called ridges) </li></ul><ul><li>process of sea-floor spreading </li></ul>Magma Ridge New crust Sea-floor spreading Asthenosphere Lithosphere Sea-floor spreading
  14. 14. <ul><li>crust descends into mantle & is recycled </li></ul><ul><li>occurs at converging boundaries (called trenches) </li></ul><ul><li>process called subduction </li></ul>Destroying crust Asthenosphere Subducting plate Trench
  15. 15. Making crust + destroying crust = conveyor belt system = rock cycle (sort of) Convection or Buoyancy Ridge push Slab pull Convection cell in mantle
  16. 16. Where are ridges & trenches? ridges trenches
  17. 17. Geologic Excitement at Tectonic Plate Boundaries
  18. 18. Global Seismicity
  19. 19. Active Volcanoes
  20. 20. 3 Major plate boundaries <ul><li>Spreading </li></ul><ul><ul><li>plates pulling apart </li></ul></ul><ul><li>Converging </li></ul><ul><ul><li>plates pushing together </li></ul></ul><ul><li>Transform </li></ul><ul><ul><li>plates sliding past each other </li></ul></ul>
  21. 21. 1. Spreading boundaries <ul><li>also called divergent boundaries </li></ul><ul><li>includes ridges and rift valleys </li></ul><ul><li>e.g. Mid-Atlantic ridge, Great Rift Valley </li></ul>
  22. 24. 2. Converging <ul><li>3 types </li></ul><ul><li>A. Oceanic -Continental  volcanic ranges </li></ul><ul><ul><li>e.g. Andes </li></ul></ul><ul><li>B. Oceanic-Oceanic  volcanic island arcs </li></ul><ul><ul><li>e.g. Japan, Aleutian islands </li></ul></ul><ul><li>C. Continental-Continental  mountain ranges </li></ul><ul><ul><li>e.g. Alps, Himalayas </li></ul></ul>
  23. 25. Convergent boundaries Oceanic -Continental Oceanic-Oceanic Continental-Continental
  24. 26. 3. Transform boundaries <ul><li>associated w/ major seismic activity </li></ul><ul><li>e.g. San Andreas system </li></ul>
  25. 27. Continental Drift Animation based on paleomaps from University of Texas Arlington http://www.ucmp.berkeley.edu/geology/anim1.html
  26. 28. Plate tectonics: predicting the future
  27. 29. Plate tectonics in the future: 50 my <ul><li>Australia will straddle the equator </li></ul><ul><li>E. Africa will form new continent </li></ul><ul><li>Mediterranean will close off </li></ul><ul><li>Atlantic Ocean will grow </li></ul><ul><li>Pacific Ocean will shrink </li></ul>

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