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Earth Science, 10e. Edward J. Tarbuck & Frederick K. Lutgens . Plate Tectonics Chapter 7. Earth Science, 10e Stan Hatfield and Ken Pinzke Southwestern Illinois College. Continental drift: an idea before its time . Alfred Wegener First proposed hypothesis, 1915

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earth science 10e

Earth Science, 10e

Edward J. Tarbuck & Frederick K. Lutgens

plate tectonics chapter 7

Plate TectonicsChapter 7

Earth Science, 10e

Stan Hatfield and Ken Pinzke

Southwestern Illinois College

continental drift an idea before its time
Continental drift: an idea before its time
  • Alfred Wegener
    • First proposed hypothesis, 1915
    • Published The Origin of Continents and Oceans
  • Continental drift hypothesis
    • Supercontinent called Pangaea began breaking apart about 200 million years ago
    • Continents "drifted" to present positions
    • Continents "broke" through the ocean crust
continental drift an idea before its time1
Continental drift: an idea before its time
  • Wegener\'s continental drift hypothesis
    • Evidence used by Wegener
      • Fit of South America and Africa
      • Fossils match across the seas
      • Rock types and structures match
      • Ancient climates
    • Main objection to Wegener\'s proposal was its inability to provide a mechanism
plate tectonics the new paradigm
Plate tectonics: the new paradigm
  • More encompassing than continental drift
  • Associated with Earth\'s rigid outer shell
    • Called the lithosphere
    • Consists of several plates
      • Plates are moving slowly
      • Largest plate is the Pacific plate
      • Plates are mostly beneath the ocean
plate tectonics the new paradigm1
Plate tectonics: the new paradigm
  • Asthenosphere
    • Exists beneath the lithosphere
    • Hotter and weaker than lithosphere
    • Allows for motion of lithosphere
  • Plate boundaries
    • All major interactions among plates occur along their boundaries
convergent continental to continental
Convergent: Continental to Continental

Convergent plate boundaries (destructive margins)

  • Definition:When subducting plates contain continental material, two continents collide
    • How they move: two continental plates push each other up
    • Landform Results: new mountain ranges
    • Example: Himalayas
    • Density: Same density so they both push each other up
convergent plate boundaries oceanic to continental
Convergent Plate Boundaries: Oceanic to Continental

Convergent plate boundaries (destructive margins)

  • Oceanic-continental convergence
    • Definition: an oceanic plate and continental plate colliding
    • How they move:oceanic plate slides underneath continental plateDenser oceanic slab sinks into the asthenosphere
    • Land formations: Pockets of magma develop and rise, continental volcanic arcs form, chain of volcanic islands
    • Examplesinclude the Andes, Cascades, and the Sierra Nevadan system
convergent plate boundaries oceanic to oceanic
Convergent Plate Boundaries: Oceanic to Oceanic
  • Oceanic-oceanic convergence
    • Definition: Two oceanic slabs converge and one descends beneath the other
    • How they move: Often forms volcanoes on the ocean floor
    • Land formation results:Volcanic island arcs forms as volcanoes emerge from the sea
    • Examples: include the Aleutian, Mariana, and Tonga islands,
    • Density: same
divergent plate boundaries
Divergent Plate Boundaries

Divergent plate boundaries (constructive margins)

  • Definition: Two plates move apart
  • How they move: Mantle material upwells to create new seafloor
  • Landform Results: Ocean ridges and seafloor spreading
    • Oceanic ridges develop along well-developed boundaries
    • Along ridges, seafloor spreading creates new seafloor
  • Examples: Iceland, and East Africa
  • Density: Same density
transform boundaries
Transform Boundaries
  • Definition: Plates slide past one another, horizontally (side to side)
    • No new crust is created
    • No crust is destroyed
  • How they move: At the time of formation, they roughly parallel the direction of plate movement
    • Aid the movement of oceanic crustal material
  • Examples: San Andres fault in California
  • Density: Plates have the same density
plate tectonics the new paradigm2
Plate tectonics: the new paradigm
  • Evidence for the plate tectonics model
    • Paleomagnetism
      • Probably the most persuasive evidence
      • Ancient magnetism preserved in rocks
      • Paleomagnetic records show
        • Polar wandering (evidence that continents moved)
        • Earth\'s magnetic field reversals
          • Recorded in rocks as they form at oceanic ridges
plate tectonics the new paradigm3
Plate tectonics: the new paradigm
  • Evidence for the plate tectonics model
    • Earthquake patterns
      • Associated with plate boundaries
      • Deep-focus earthquakes along trenches provide a method for tracking the plate\'s descent
    • Ocean drilling
      • Deep Sea Drilling Project (ship: Glomar Challenger)
plate tectonics the new paradigm4
Plate tectonics: the new paradigm
  • Evidence for the plate tectonics model
    • Hot spots
      • Rising plumes of mantle material
      • Volcanoes can form over them
        • e.g., Hawaiian Island chain
        • Chains of volcanoes mark plate movement
plate tectonics the new paradigm5
Plate tectonics: the new paradigm
  • Evidence for the plate tectonics model
    • Ocean drilling
      • Age of deepest sediments
        • Youngest are near the ridges
        • Older are at a distance from the ridge
      • Ocean basins are geologically young
plate tectonics the new paradigm6
Plate tectonics: the new paradigm
  • Measuring plate motion
    • By using hot spot “tracks” like those of the Hawaiian Island - Emperor Seamount chain
    • Using space-age technology to directly measure the relative motion of plates
      • Very Long Baseline Interferometry (VLBI)
      • Global Positioning System (GPS)
plate tectonics the new paradigm7
Plate tectonics: the new paradigm
  • Driving mechanism of plate tectonics
    • No one model explains all facets of plate tectonics
    • Earth\'s heat is the driving force
    • Several models have been proposed
      • Slab-pull and slab-push model
        • Descending oceanic crust pulls the plate
        • Elevated ridge system pushes the plate
plate tectonics the new paradigm8
Plate tectonics: the new paradigm
  • Driving mechanism of plate tectonics
    • Several models have been proposed
      • Plate-mantle convection
        • Mantle plumes extend from mantle-core boundary and cause convection within the mantle
        • Models
          • Layering at 660 kilometers
          • Whole-mantle convection
          • Deep-layer model
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