Plate Tectonics

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Plate Tectonics

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Earths Lithospheric Crust

• Divided into large and small crustal plates
• Makes up the ocean floor and the continental land
  masses, along with the upper mantle.

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The oceanic crust averages 8 km deep but is dense
enough to support the continental crust riding on
it. The continental crust averages 35 km deep
both are relatively thin.
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The crust covers a thick molten, moving mantle
(68 of the earths volume) and a heavy core,
composed of nickel and iron. The plate move in
different directions resulting in the cracking of
the crust.
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Major plate boundaries can be mapped using
seismic activity.
Live Seismic Activity
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The Major Plates
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Plate Boundaries

• What happens when plates meet?

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Oceanic to Oceanic boundary divergent

• Both plates are composed of basalt, also Mg, Fe,
  and Si
• Both are made of high density rock
• The result is a vent, mid-ocean ridge is and
  example.

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Continental to Continental boundary - convergent

• Both plates are granite, also Si and AL
• Plates have low density rock
• The result is that edges are forced up into
  mountains.

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Oceanic to Continental boundary a convergent,
subduction zone, plate edges over-ride or slide
past others

• Lighter continental plate edge override the
  denser oceanic plate
• Oceanic plate edge are subducted down into the
  asthenosphere and are re-melted
• The result - Trenches

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What the Boundaries Look Like
Convergent Plate Boundaries
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Transform Fault Boundary
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Whats at the boundary lines?
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1912, Alfred Wegner proposed the idea of a
super-continent called Pangaea that broke apart
to form todays land masses

• The Reasons
• The continents shape roughly fit together
• The rocks and fossils of different continents
  matched

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Harry Hess and J Wilson propose a mechanism to
explain continental movement in the early 60s.
to avoid criticism the termed it geo-poetry

• In 1969 the Glomar Challenger drilled a series of
  holes in the Mid-Atlantic ridge. What they found
  changed geology and oceanography.

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Continental Rocks date the Earth at about 5
billion years old. Since the ocean floor is lower
in the lithosphere, scientists expected to find
older rocks at those depths.Continental
geologys law of Superposition states that oldest
rocks are laid down first and should be found
horizontally lowest in a bed unless uplifted.
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They found no rock older than 3 billion years and
most were younger. How could the ocean floor be
younger than the continents riding on it?
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The Deep Sea Drilling project showed that rocks
became older as they moved away from the mid
ocean ridge. Oceanic geology showed rock layers
are created vertically.The MOR seemed to be a
parallel distance from continents on either side.
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Core samples revealed matching striping in rocks
on both sides of the MOR.
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In 1977, Project FAMOUS photographed magma
squeezing out of the MOR and creating new ocean
floor.
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Scientists, Mathews and Vine had data for a
cohesive theory on plate tectonics. The sea floor
was spreading moving continents with it. The
theory of sea floor spreading explained
continental drift. Proving Wegner to be correct.