Earth science 10e
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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


Pangaea approximately 200 million years ago

Pangaea approximately 200 million years ago


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


Wegener s matching of mountain ranges on different continents

Wegener’s matching of mountain ranges on different continents


Paleoclimatic evidence for continental drift

Paleoclimatic evidence for Continental Drift


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


A continental continental convergent plate boundary

A continental-continental convergent plate boundary


The collision of india and asia produced the himalayas before

The collision of India and Asia produced the Himalayas (before)


The collision of india and asia produced the himalayas after

The collision of India and Asia produced the Himalayas (after)


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


An oceanic continental convergent plate boundary

An oceanic-continental convergent plate boundary


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


An oceanic oceanic convergent plate boundary

An oceanic-oceanic convergent plate boundary


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


Divergent boundaries are located mainly along oceanic ridges

Divergent boundaries are located mainly along oceanic ridges


The east african rift a divergent boundary on land

The East African rift – a divergent boundary on land


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


Apparent polar wandering paths for eurasia and north america

Apparent polar-wandering paths for Eurasia and North America


Paleomagnetic reversals recorded by basalt flows at mid ocean ridges

Paleomagnetic reversals recorded by basalt flows at mid-ocean 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)


Distribution of earthquake foci at plate boundaries

Distribution of earthquake foci at plate boundaries


Earthquake foci in the vicinity of the japan trench

Earthquake foci in the vicinity of the Japan trench


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


The hawaiian islands have formed over a stationary hot spot

The Hawaiian Islands have formed over a stationary hot spot


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)


Directions and rates of plate motions

Directions and rates of plate motions


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


Layering at 660 kilometers

Layering at 660 kilometers


Whole mantle convection

Whole-mantle convection


Deep layer model

Deep-layer model


End of chapter 7

End of Chapter 7


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