Ch7_Plate_Tectonics_students
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  • 1. CH. 8 – PLATE TECTONICS
  • 2. Continental Drift
    • 1915:
    • Alfred Wegener
    • - hypothesized the supercontinent Pangaea (“all land”)
  • 3. Plate Tectonics
    • WWII
    • New technology = echosounder
    • -used to map ocean floor topography
  • 4. Harry Hess
    • 1962:
    • Hypothesized sea-floor spreading
  • 5. Sea-floor spreading
    • a) Ocean crust splits apart at mid-ocean ridges (MOR)
    • - pushes continents away from each other
  • 6. Sea-floor spreading
    • b) Ocean crust pulled down into mantle at deep-sea trenches
    • New idea : ocean crust is moving!
  • 7. Plate dynamics
  • 8. Evidence for sea-floor spreading (late 1960’s - 1970’s)
    • 1) Deep-sea Drilling Projects
      • Glomar Challenger
      • Discovered:
      • a) Ocean crust is __________
  • 9. Deep-sea drilling projects
    • b) Sediment thickness varies:
    • - thicker further away from MOR
    • c) Sediment age:
    • - increases with distance from MOR
  • 10. 2) Submersible Expeditions
    • 1974 FAMOUS expedition
    • ( F rench- A merican M id- O cean U ndersea S tudy)
  • 11. Submersible Expeditions
    • Evidence for mafic eruptions:
      • - hydrothermal vents (~350 o C)
      • - pillow lavas
  • 12. Problem:
    • How does crust move over solid rock of mantle?
  • 13. 3) Clues: seismic waves
    • Lithosphere – rigid rx of crust and uppermost mantle
    • Asthenosphere – weaker rocks (partially molten) in upper mantle
  • 14.  
  • 15. Plate Tectonics Theory
    • Plate – rigid slab of lithosphere
    • 7 major plates on Earth
    • Each plate moves independently
  • 16. Plate map
  • 17. Same plate
    • Locations do not change position relative to one another
    • Ex: NYC & Peoria always same distance apart
  • 18. Different plates
    • Locations do change position relative to one another
    • Ex: NYC & London getting further apart
  • 19. Plate Boundaries
    • Identified by geologic activity:
    • 1) Earthquakes
    • 2) Volcanism
    • - mid-ocean ridges
    • - circum-Pacific belt
  • 20. EQ Foci Volcanic Activity
  • 21. Plate Boundaries
    • 3) Mountain Ranges
    • - indicates plate collisions
    • 4) Deep-Sea Trenches
    • Subduction = one plate “dives” beneath another
  • 22. Subduction
    • Marked by Benioff Zone
    • - line of shallow- to deep-focus EQ’s along a deep-sea trench
  • 23. Subduction zone EQ foci
  • 24. Deep-Sea Trenches
    • NOTE : Most trenches located in Pacific Ocean
    • Atlantic Ocean is predominately a spreading center
    • Plates converge on Pacific Ocean side
  • 25. Types of Plate Boundaries
    • 1) Divergent – plates pull away from each other
    • Characteristics:
    • a) shallow-focus EQ’s
    • b) mafic magma
    • c) rift valleys
  • 26. Divergent Plate Boundaries
      • b) mid-ocean ridges
      • Ex: Iceland
      • b) continental rift valleys
      • Ex: East African Rift Valley
      • Red Sea
  • 27. Close-up of Africa
  • 28. Types of Plate Boundaries
    • 2) Convergent – plates collide
    • 3 subtypes:
    • a) Ocean-Continental
    • - ocean plate subducted beneath continental plate
  • 29. Ocean-Continent Convergent
  • 30. Ocean-Continental Convergent
    • Characteristics :
    • Deep-sea trenches parallel continent
    • Benioff Zone
  • 31. Ocean-Continental Convergent
    • Volcanic arcs on continental margin
    • - source of magma is melting plate
    • - composite cones
    • Ex: Andes Mtns., S. America
    • Peru-Chile Trench
    • Cascade Mtns., N. America
  • 32. Types of Convergent Boundaries
    • b) Ocean-ocean
    • Denser ocean plate is subducted
  • 33. Ocean-Ocean Convergent
    • Characteristics :
    • Deep-sea trench
    • Benioff Zone
    • Volcanic island arcs (composite cones)
  • 34. Ocean-Ocean Convergent
    • Ex: Japanese Islands
    • Aleutian Islands
    • Caribbean Islands
    • Indonesia
  • 35. Types of Convergent Boundaries
    • c) Continent to Continent
    • Characteristics :
    • Shallow-focus EQ’s only
    • No volcanism
    • Complex folded mountains
  • 36.  
  • 37. Continent-Continent Convergent
    • Ex: Himalayan Mtns. (active)
    • Appalachian Mtns. (inactive)
  • 38. India into Asia Himalayan Mountains
  • 39. Types of Plate Boundaries
    • 3) Transform- plates slide laterally
    • Characteristics :
    • - shallow-focus EQ’s only
    • - crust neither created nor destroyed
  • 40.  
  • 41. Transform Boundary
    • Ex: San Andreas Fault
    • North American Plate meets Pacific Plate
  • 42. Hot Spot Volcanism (handout)
    • Associated with intraplate volcanism
    • Hot spots are stationary w/in mantle (“mantle plume”)
  • 43. Mantle plume
  • 44.  
  • 45. Exam 3
    • EQ & Plate Tectonic Study Guide
    • Map on back of PT Study Guide
    • Know: plate boundaries
    • characteristics
    • locations