Plate Tectonics

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Plate Tectonics

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Theory of Plate Tectonics

• Meaning plate structure
• Developed 1960s (50 years after Wegener)
• The Earth is divided into approximately 9 major
  plates.
• Explains the movement of Earths plates, causes
  of volcanoes, earthquakes, ocean trenches,
  mountain formation, and other geological
  phenomena.

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• Plates move about 1-10 cm per year!!!
• Seismic activity (volcanoes and earthquakes)
  occur as plate boundaries interact.

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Plate Boundaries

• There are 3 types of plate boundaries
• Divergent
• Convergent
• Transform

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Divergent movement of 2 plates away from
each other
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Convergent colliding of 2 plates
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Transform plates sliding horizontally past each
other.
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Earths Major Plates

• Eurasian Caribbean
• Australian-Indian South American
• Pacific African
• Juan de Fuca Antarctic
• North American

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Earths Major Plates
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Crust

• Oceanic thin, under ocean crust is thin and is
  very dense, active
• Continental thick, under land, constantly
  created and destroyed.

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Remember, Wegner did not have a reason why the
continents moved apart, lets investigate this!
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Sea- floor Spreading

• The longest chain of mountains in the world is
  the Mid-Ocean Ridge.
• Scientists have mapped the ocean floor and
  mid-ocean ridge using S.O.N.A.R.
• The mid-ocean ridge extends into all of Earths
  oceans.
• The Island of Iceland is part of the ridge that
  rises above the surface in the Atlantic Ocean.
• Down the middle of the ridge is an area called
  the rift valley It is almost twice as deep as
  the Grand Canyon

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Harry Hess

• Harry Hess examined maps of the mid-ocean ridge
  and proposed that the ocean floors move like
  conveyor belts, carrying the continents along
  with them.
• This movement begins at the Mid- Ocean Ridge.
• At the ridge, the molten material rises from the
  mantle and erupts (much like a volcano).
• The oldest rock is farthest from the center of
  the ridge.
• Harry Hess first proposed the idea of Sea-Floor
  Spreading.

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Evidence for Sea-Floor Spreading

• Molten Material. The submersible ALVIN was sent
  down to study the rift valley.

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Evidence

• Rock Sampling. The Glomar Challenger was a
  drilling ship the gathered samples from the ocean
  floor.
• The scientists determined the age- of the rocks
  in the samples and found that the farther-away
  from the ridge, the older the rocks were.
• The oldest rocks are about 4 million years old.
• The newer rocks were always in the center of the
  ridges

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Evidence

• Magnetic Stripes. How does the pattern of
  matching stripes show evidence of sea-floor
  spreading?

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How does the ocean floor keep getting wider

• The ocean floor plunges into deep under water
  trenches.
• A deep ocean trench forms where the oceanic crust
  collides with continental crust.
• Subduction is the process by which the ocean
  floor sinks beneath a deep-ocean trench and back
  into the mantle.

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FYI

• Most ocean trenches are found in the Pacific
  Ocean.
• The deepest part of the ocean is the Mariannas
  Deep. It is located in the Pacific Ocean
• The Pacific Ocean is shrinking, but it is still
  the Largest ocean