Plate Tectonics. The Continental Drift Hypothesis Plate Tectonics – Overview Divergent Boundaries Convergent Boundaries Transform Boundaries Testing the

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  • Plate Tectonics

  • Plate TectonicsThe Continental Drift HypothesisPlate Tectonics OverviewDivergent BoundariesConvergent BoundariesTransform BoundariesTesting the Theory of Plate TectonicsMeasuring Plate MotionWhat Makes Plates Move?

  • The Continental Drift HypothesisGEOL131: Plate Tectonics

  • Alfred Wegener (1880-1930)German paleoclimatologistStudied evidence for ancient climates

    Traveled extensively, collected thousands of samples

    Published continental drift ideas in 1915

    Died during expedition to Greenland in 1930

    GEOL131: Plate Tectonics: Continental Drift

  • PangaeaAll lands200 million years ago

    GEOL131: Plate Tectonics: Continental Drift

  • Wegeners EvidenceThe continental jigsaw puzzle

    Trans-oceanic fossil matching

    Trans-oceanic rock matching

    Ancient climates

    GEOL131: Plate Tectonics: Continental Drift

  • Wegeners Evidence: Continental JigsawGEOL131: Plate Tectonics: Continental Drift

  • Wegeners Evidence: Matching FossilsGEOL131: Plate Tectonics: Continental Drift

  • Wegeners Evidence: Matching FossilsGEOL131: Plate Tectonics: Continental Drift

  • Wegeners Evidence: Matching RocksGEOL131: Plate Tectonics: Continental DriftPresentPangaea

  • Wegeners Evidence: Ancient ClimatesGEOL131: Plate Tectonics: Continental DriftPresentPangaea

  • Other scientists were highly critical

    Major problem: no good explanation for how continents could move

    Wegener proposedMoons gravity moved continentsContinents pushed through ocean crust like icebreaker shipsReaction to Wegeners IdeasGEOL131: Plate Tectonics: Continental Drift

  • Moons gravity too weak

    Ocean crust too dense and strong

    Most scientists concluded continental drift was incorrectReaction to Wegeners IdeasGEOL131: Plate Tectonics: Continental Drift

  • Plate Tectonics: OverviewGEOL131: Plate Tectonics

  • Based on compositionCrust, mantle, core

    Based on seismic wave behaviorLithosphere, asthenosphere, mesosphere, outer core, inner core

    Lithosphere, asthenosphere most important for plate tectonicsEarths Layers: Two schemesGEOL131: Plate Tectonics: Plate Tectonics Overview

  • Earths Layers: Two schemesGEOL131: Plate Tectonics: Plate Tectonics OverviewAsthenosphere

  • Rigid, brittle

    Continents are embedded in them

    Lithospheric PlatesGEOL131: Plate Tectonics: Plate Tectonics Overview

  • Provides plausible explanation for how continents move

    Doesnt require them to plow through ocean crust

    Why is plate tectonic theory successful?GEOL131: Plate Tectonics: Plate Tectonics Overview

  • OceanicThin, dense, able to subduct into mantleasphalt

    ContinentalThick, low density, buoyant, does not subductstyrofoamTwo types of lithosphereGEOL131: Plate Tectonics: Plate Tectonics Overview

  • Plate MotionGEOL131: Plate Tectonics: Plate Tectonics Overview

  • Plate Boundaries: DivergentGEOL131: Plate Tectonics

  • Plates separate at divergent boundariesGEOL131: Plate Tectonics: Divergent BoundariesNew crust created by undersea volcanism

  • Creation of Divergent BoundariesGEOL131: Plate Tectonics: Divergent Boundaries1. Continental lithosphere pushed up by upwelling magma2. Lithosphere stretched & thinned, forming a continental rift

  • Creation of Divergent BoundariesGEOL131: Plate Tectonics: Divergent Boundaries3. Ocean water floods rift, creating narrow seaway4. Seaway continues to widen as plates separate

  • Creation of Divergent BoundariesGEOL131: Plate Tectonics: Divergent BoundariesStage 1: Yellowstone NP - Continental lithosphere being pushed up by magma below

  • Creation of Divergent BoundariesGEOL131: Plate Tectonics: Divergent BoundariesStage 2: East African Rift - Lithosphere being stretched and thinnedStage 3: Red Sea and Gulf of Aden- Narrow seaways

  • Creation of Divergent BoundariesGEOL131: Plate Tectonics: Divergent BoundariesStage 4: Atlantic Ocean wide ocean basin with divergent boundary at center

  • Plate Boundaries: ConvergentGEOL131: Plate Tectonics

  • Three types, based on lithosphere involvedOceanic-oceanicOceanic-continentalContinental-continentalPlates come together at convergent boundariesGEOL131: Plate Tectonics: Convergent Boundaries

  • Oceanic-oceanic boundariesGEOL131: Plate Tectonics: Convergent Boundaries

  • Oceanic-continental boundariesGEOL131: Plate Tectonics: Convergent Boundaries

  • Continental-continental boundariesGEOL131: Plate Tectonics: Convergent BoundariesA.k.a. continental collision zones

    Example: India and Asia

  • India-Asia Collision: Example of a continent-continent convergent boundaryGEOL131: Plate Tectonics: Convergent Boundaries

  • Plate Boundaries: TransformGEOL131: Plate Tectonics

  • Plates slide past each other at transform boundariesGEOL131: Plate Tectonics: Transform Boundaries

  • San Andreas Fault: A transform boundaryGEOL131: Plate Tectonics: Transform BoundariesLos Angeles is moving northwest

    San Francisco is moving southeast

  • San Andreas Fault: A transform boundaryGEOL131: Plate Tectonics: Transform Boundaries

  • Testing the Plate Tectonic TheoryGEOL131: Plate Tectonics

  • Much evidence comes from ocean drillingGEOL131: Plate Tectonics: Testing the Plate Tectonic TheoryResearch ships drill into ocean sediments and rock

    Drill cores are collected that show cross-section of ocean floor at that location

  • Major Lines of EvidenceGEOL131: Plate Tectonics: Testing the Plate Tectonic TheorySediment thicknessesOcean crust agesHot spot tracksApparent polar wanderingPaleomagnetic striping

  • Sediment Thickness and Crustal AgeGEOL131: Plate Tectonics: Testing the Plate Tectonic TheoryBoth increase away from oceanic ridges

  • Hot Spot TracksGEOL131: Plate Tectonics: Testing the Plate Tectonic Theory

  • Apparent Polar WanderingGEOL131: Plate Tectonics: Testing the Plate Tectonic TheoryEarth has a magnetic field

    Some minerals are magnetic

    These minerals act like compass needlesThey record where magnetic poles were located at the time the minerals formed

  • Apparent Polar WanderingGEOL131: Plate Tectonics: Testing the Plate Tectonic TheoryRocks in North America and Eurasia seem to show that magnetic poles have moved thousands of miles

    Continents have moved, not the poles

  • Paleomagnetic StripingGEOL131: Plate Tectonics: Testing the Plate Tectonic TheoryEarths magnetic field has reversed many timesNormal polarity: North magnetic pole near north geographic pole

    Reversed polarity: N. magnetic near S. geographic

    Magnetic field polarities over the last 4 million years. Periods of normal polarity shown in white.

  • Paleomagnetic StripingGEOL131: Plate Tectonics: Testing the Plate Tectonic Theory

    Oceanic crustal rocks record the polarity in effect at the time they formed

    Symmetrical stripe pattern of normal and reversed polarity created in ocean crust

  • What Makes Plates Move?GEOL131: Plate Tectonics

  • Three mechanisms: slab pull, ridge push, mantle dragGEOL131: Plate Tectonics: What Makes Plates Move?***

  • End of ChapterGEOL131: Plate Tectonics