Fathoms Below / Under the Sea



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tarix13.12.2017
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Fathoms Below / Under the Sea

  • Fathoms Below / Under the Sea

  • From soundtrack of Disney’s The Little Mermaid






Plate Tectonic Boundaries

  • Plate Tectonic Boundaries





Alfred Wegener -1912

  • Alfred Wegener -1912

  • Wegener not able to provide MECHANISM for his theory

  • Major mechanism later found in the OCEANS



Harry Hess - 1960s

  • Harry Hess - 1960s

    • new ocean basins form from volcanism
    • ocean floor forms IN BETWEEN pieces that have split
    • SEAFLOOR SPREADING


Theoretical breakthrough

  • Theoretical breakthrough

    • PLATE TECTONICS
    • surface of earth composed of “plates” (LITHOSPHERE) that move on a “conveyor belt” (ASTHENOSPHERE)




Fit of the continents

  • Fit of the continents

  • Correlation of mountain belts

  • Diversity of species

    • correlation of dinosaur species (Pangea)
    • isolation of mammal species (after breakup)
  • Glaciers



“Relationships known since early in the century yet the validity of continental drift was not generally recognized until the late 1960’s”

  • “Relationships known since early in the century yet the validity of continental drift was not generally recognized until the late 1960’s”

  • It took ocean floor data to solidify ideas and convince scientific community!

  • The oceans rule!





seafloor-spreading

  • seafloor-spreading

  • lithosphere

  • asthenosphere





subduction

  • subduction

  • world’s most explosive volcanos are formed over subduction zones

  • Oregon’s Cascades Mtns. over Cascadia Subduction Zone

    • Juan de Fuca plate under N. American plate


“MUNCH” - subduction of oceanic plate under continent or ocean

  • “MUNCH” - subduction of oceanic plate under continent or ocean

  • “CRUNCH” - collision of continental plates

    • India into Tibet and China
    • continental crust is thick and light




Transform faults

  • Transform faults

    • plates neither created nor destroyed
  • Transform faults are active

  • Fracture zones are inactive extensions of transforms

    • “fossil transforms”






Oldest seafloor - 200 million years

  • Oldest seafloor - 200 million years

  • Oldest land - billions of years

  • With seafloor spreading, is the earth expanding?

  • Why is seafloor so young relative to continents?

  • SUBDUCTION

  • “law of conservation of ocean floor”



Convergent - subduction

  • Convergent - subduction

    • trenches
    • Tonga Trench, Cascadia Subduction Zone


Divergent - seafloor spreading

  • Divergent - seafloor spreading

    • mid-ocean ridges or rises
    • Mid-Atlantic RIDGE, East Pacific RISE


Translational - strike-slip faulting

  • Translational - strike-slip faulting



How do we know where these boundaries are?

  • How do we know where these boundaries are?

  • bathymetry

  • earthquakes

  • deepest earthquakes at CONVERGENT boundaries (subduction zones/trenches)

  • downgoing plate breakage causes earthquake

  • like potato chip breaking off in bean dip









What made people believe in seafloor spreading? (poor Wegener!)

  • What made people believe in seafloor spreading? (poor Wegener!)

  • changes in inclinations of magnetic field

  • Earth’s magnetic field a mystery

  • currents in liquid core one hypothesis





Earth’s magnetic field flips back & forth

  • Earth’s magnetic field flips back & forth

  • magma freezes magnetic minerals

  • minerals lines themselves up w/ prevailing field of earth

  • anomaly in field is the key - normal (positive) or reversed (negative)

  • Vine and Matthews noted this in the ‘60s and flagged this as PROOF for seafloor spreading













“Slab pull” versus “ridge push”

  • “Slab pull” versus “ridge push”



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