Continental Drift / Plate Tectonics

• The Puzzle
  • Alfred Wegener "Continental Drift" hypothesis
    • obvious jigsaw puzzle
      • matched geology and coastlines
    • Scandinavian & British Isles mountains matched Appalachian mtns.
    • Mesosaurus fossils found in both South America and Africa
      
      
• Evidence
  • oceanic mapping efforts (1940's - 60's)
    • mid-oceanic ridges (shape)
    • magnetic reversals (symmetrical bands)
    • rock's age increases outward (dating rocks)
      
      
• Explanation (cause)
  
• concept of convection to explain continental drift
  • rise of new crustal material at mid-oceanic ridges
  • conveyor belt movement
    • now known as sea-floor speading
      
      
      
• Plates and Movement
  • 20 major plates moving as distinct units (see map)
    
  • lighter continental plates and heavier and thinner oceanic plates
    
    
  • Diverge at mid-ocean (divergence)
    • Pacific & Atlantic Ocean
      • new crust being formed
        
        
  • diverge on continents
    • Great East African Rift Valley
      
      
      
  • Lateral movement - plates slide past one another
    • "transform faults" - lateral movement of plates
      • Example: San Andreas Fault
        
        
  • Converge where plates slowly collide into one another
  • South Asian Continent
    • continental - continental convergence
      • Himalayan Mountains
        
        
• "Subduction" - where plates slide under one another
  • associated with volcanoes and earthquakes
    • Pacific Ring of Fire
      • oceanic - continental convergence
    • Andes Mountains
    • Cascades in the Pacific Northwest
    • oceanic - oceanic convergence
      • Aleutian Islands