Lecture10 platetectonics
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  • 1. Plate Tectonics Tectonic Plates of the Earth
  • 2. How can we explain the rock cycle?
    • Need to identify mechanisms by which rocks are
      • Heated and melted
      • Buried and metamorphosed
      • Pushed up into mountains to be eroded
  • 3. Earth as a jigsaw puzzle
    • Matching continental edges: recognized for centuries
    • Pangaea: supercontinent proposed by Wegener (1912)
  • 4. Wegener’s contribution
    • continental drift
    • = pattern of moving continents
  • 5. Theory of fixed continents
    • Traditional assumption: continents & ocean basins fixed in position
    • Problems
    • Matching continent edges
    • Matching fossils among continents
    • Matching geology among continents
  • 6. Evidence against fixed continents Matching edges Matching geology
  • 7. Bathymetry of the ocean floor continental shelf abyssal plain trench mid ocean ridge
  • 8. Thickness of the Sediment x 550 m x 102 m x 18 m x 112 m x 430 m 35 m x
  • 9. The Driving Mechanism
  • 10. Paleomagnetism
  • 11. Radiometric dating Red = younger, green = older
  • 12. Plate tectonics
    • = process for continental drift
    • Thermal convection system within Earth
      • 1. Making crust
      • 2. Destroying crust
      • Explains the rock cycle!
  • 13. Making crust
    • magma rises up from mantle, spreads out, & cools
    • occurs at spreading boundaries (called ridges)
    • process of sea-floor spreading
    Magma Ridge New crust Sea-floor spreading Asthenosphere Lithosphere Sea-floor spreading
  • 14.
    • crust descends into mantle & is recycled
    • occurs at converging boundaries (called trenches)
    • process called subduction
    Destroying crust Asthenosphere Subducting plate Trench
  • 15. Making crust + destroying crust = conveyor belt system = rock cycle (sort of) Convection or Buoyancy Ridge push Slab pull Convection cell in mantle
  • 16. Where are ridges & trenches? ridges trenches
  • 17. Geologic Excitement at Tectonic Plate Boundaries
  • 18. Global Seismicity
  • 19. Active Volcanoes
  • 20. 3 Major plate boundaries
    • Spreading
      • plates pulling apart
    • Converging
      • plates pushing together
    • Transform
      • plates sliding past each other
  • 21. 1. Spreading boundaries
    • also called divergent boundaries
    • includes ridges and rift valleys
    • e.g. Mid-Atlantic ridge, Great Rift Valley
  • 22.  
  • 23.  
  • 24. 2. 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
  • 25. Convergent boundaries Oceanic -Continental Oceanic-Oceanic Continental-Continental
  • 26. 3. Transform boundaries
    • associated w/ major seismic activity
    • e.g. San Andreas system
  • 27. Continental Drift Animation based on paleomaps from University of Texas Arlington http://www.ucmp.berkeley.edu/geology/anim1.html
  • 28. Plate tectonics: predicting the future
  • 29. 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