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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 continentsnew 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 continentsnew 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 continents

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 (after)

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 (after)

  • 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 (after)

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



The east african rift a divergent boundary on land
The East African rift – a (after)divergent boundary on land


Transform boundaries
Transform Boundaries (after)

  • 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 (after)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 mid-ocean ridgesnew 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)


Distribution of earthquake foci at plate boundaries
Distribution of earthquake mid-ocean ridgesfoci at plate boundaries


Earthquake foci in the vicinity of the japan trench
Earthquake foci in the vicinity mid-ocean ridgesof the Japan trench


Plate tectonics the new paradigm4
Plate tectonics: the mid-ocean ridgesnew 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 mid-ocean ridgesnew 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 mid-ocean ridgesnew 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)


Directions and rates of plate motions
Directions and rates mid-ocean ridgesof plate motions


Plate tectonics the new paradigm7
Plate tectonics: the mid-ocean ridgesnew 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 mid-ocean ridgesnew 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


Layering at 660 kilometers
Layering at 660 kilometers mid-ocean ridges


Whole mantle convection
Whole-mantle convection mid-ocean ridges


Deep layer model
Deep-layer model mid-ocean ridges


End of chapter 7

End of Chapter 7 mid-ocean ridges