Theory of Plate Tectonics

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Theory of Plate Tectonics

• Plate Tectonics
• Plate Boundaries
• Causes of Plate Tectonics

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Plate Tectonics
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What is Plate Tectonics

• The Earths crust and upper mantle are broken
  into sections called plates.
• Plates move around on top of the mantle like
  rafts.

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What is the Lithosphere?

• The crust and part of the upper mantle
  lithosphere
• 100 km thick
• Less dense than the material below it so it
  floats

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What is the Asthenoshere?

• The plastic layer below the lithosphere
  asthenosphere
• The plates of the lithosphere float on the
  asthenosphere.

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2 Types of Plates

• Oceanic plates - plates below the oceans.
• Contain mostly basalt.
• Continental plates - plates below the continents.
• Contain mostly rhyolite.

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Plate Boundaries
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Divergent Boundaries

• Boundary between two plates that are moving apart
  or rifting.
• ? ?
• RIFTING causes SEAFLOOR SPREADING.

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Features of Divergent Boundaries

• Mid-ocean ridges
• Rift valleys
• Fissure volcanoes

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Convergent Boundaries

• Boundaries between two plates that are colliding.
• ? ?
• There are 3 types

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Type 1

• Oceanic plate colliding with a less dense
  continental plate.
• Subduction Zone where the more dense plate
  slides under the less dense plate.
• VOLCANOES occur at subduction zones.
• Ring of Fire Animations

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Andes Mountains, South America
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Type 2

• Oceanic plate colliding with another oceanic
  plate.
• The more dense plate slides under the less dense
  plate creating a subduction zone called a TRENCH.

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Aleutian Islands, Alaska
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Type 3

• A continental plate colliding with another
  continental plate.
• Have Collision Zones
• a place where folded and thrust faulted mountains
  form.

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Transform Fault Boundaries

• Boundary between two plates that are sliding past
  each other.
• EARTHQUAKES occur along these faults.

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San Andreas Fault, CA
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Causes of Plate Tectonics
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Convection Currents

• Hot magma in the Earth moves toward the surface,
  cools, then sinks again.
• Creates convection currents beneath the plates
  that cause the plates to move.

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