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Lecture10 platetectonics
 

Lecture10 platetectonics

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    Lecture10 platetectonics Lecture10 platetectonics Presentation Transcript

    • Plate Tectonics Tectonic Plates of the Earth
    • 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
    • Earth as a jigsaw puzzle
      • Matching continental edges: recognized for centuries
      • Pangaea: supercontinent proposed by Wegener (1912)
    • Wegener’s contribution
      • continental drift
      • = pattern of moving continents
    • Theory of fixed continents
      • Traditional assumption: continents & ocean basins fixed in position
      • Problems
      • Matching continent edges
      • Matching fossils among continents
      • Matching geology among continents
    • Evidence against fixed continents Matching edges Matching geology
    • Bathymetry of the ocean floor continental shelf abyssal plain trench mid ocean ridge
    • Thickness of the Sediment x 550 m x 102 m x 18 m x 112 m x 430 m 35 m x
    • The Driving Mechanism
    • Paleomagnetism
    • Radiometric dating Red = younger, green = older
    • Plate tectonics
      • = process for continental drift
      • Thermal convection system within Earth
        • 1. Making crust
        • 2. Destroying crust
        • Explains the rock cycle!
    • 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
      • crust descends into mantle & is recycled
      • occurs at converging boundaries (called trenches)
      • process called subduction
      Destroying crust Asthenosphere Subducting plate Trench
    • Making crust + destroying crust = conveyor belt system = rock cycle (sort of) Convection or Buoyancy Ridge push Slab pull Convection cell in mantle
    • Where are ridges & trenches? ridges trenches
    • Geologic Excitement at Tectonic Plate Boundaries
    • Global Seismicity
    • Active Volcanoes
    • 3 Major plate boundaries
      • Spreading
        • plates pulling apart
      • Converging
        • plates pushing together
      • Transform
        • plates sliding past each other
    • 1. Spreading boundaries
      • also called divergent boundaries
      • includes ridges and rift valleys
      • e.g. Mid-Atlantic ridge, Great Rift Valley
    •  
    •  
    • 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
    • Convergent boundaries Oceanic -Continental Oceanic-Oceanic Continental-Continental
    • 3. Transform boundaries
      • associated w/ major seismic activity
      • e.g. San Andreas system
    • Continental Drift Animation based on paleomaps from University of Texas Arlington http://www.ucmp.berkeley.edu/geology/anim1.html
    • Plate tectonics: predicting the future
    • 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