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    Ch7_Plate_Tectonics_students Ch7_Plate_Tectonics_students Presentation Transcript

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