Plate Tectonics

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Plate Tectonics
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Plate Tectonics

• The Theory of Plate Tectonics is a theory that
  describes the formation, movements, and
  interactions of Earths lithospheric plates that
  move on the asthenosphere.

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Theory of Plate Tectonics

• The Theory of Plate Tectonics explains why
  earthquakes and volcanoes are likely to occur in
  particular locations and how new crust forms
  along the ocean floor.

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Earthquakes and volcanic activity occur primarily
at the location of plate boundaries.

• Plate boundaries are where 2 plates are pushing
  toward, pulling away, or sliding past each other.
  The strain and friction causes fractures in the
  earth, where earthquakes occur and where the
  fractures allow molten rock to flow to the
  surface.

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Evidence for plate tectonics was also found in
igneous rocks which recorded the direction of
Earths magnetic field.
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• Mid-ocean ridge is a long chain of volcanic
  mountains on the ocean floor with a deep central
  valley. The mid-ocean ridge always shows the
  magnetic orientation of the North and South
  poles.

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Mid-ocean Ridge

• A pattern of bands on either side of the
  mid-ocean ridge show the changes in magnetic
  orientation.

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Mid-ocean Ridges

• Rocks at the center of the mid-ocean ridge are
  the youngest.
• Mid-ocean ridges are boundaries where plates are
  moving apart.

(so the farther the rocks are from the mid-ocean
ridge the the rocks
are).
older
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3 Main Hypothesis Which Cause of Plate Movement

• Mantle Convection,
• Ridge Push, and
• Slab Pull

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Mantle Convection

1. Mantle Convection - the transfer (convection) of
   heat from Earths inner and outer cores moves the
   plates (like a convection belt)

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Ridge Push

• Ridge Push occurs at the Mid-ocean Ridges
• - The hot molten magma rises up at the
  mid-ocean ridges and as it cools and hardens into
  a denser rock, the rock pushes out and slides
  down the ridge, allowing more new hot molten
  material to flow out of the mid-ocean ridge.

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Slab Pull - Scientists believe this Slab Pull is
the greater factor out of the three theories.

• Slab Pull occurs at a subduction boundary.
• - The denser, heavier plate sinks underneath
  the other less dense plate. The edge of the
  subduction plate is much colder and heavier than
  the mantle, so it continues to sink and pull the
  rest of the plate along down with it.

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CONTINENTAL DRIFT

• Alfred Wegener proposed a hypothesis called
  Continental Drift which said the continents have
  drifted, or moved from one location to another
  over time.

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Continental Drift was proven by

• The shapes of the continents seem to match up
  (fit together like puzzle pieces)

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Continental Drift was proven by

• Certain fossils are on different continents
• Example Mesosaurus reptile that lived about
  270 mya, fossils found only in parts of South
  America and Africa could have only happened
  when the 2 continents were once joined).

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Continental Drift was proven by

• Mountain chains found on 2 continents and would
  have matched up if the continents were joined.
• Example Appalachian Mountains run along the
  eastern coast of US and through Great Britain.

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Pangaea the giant supercontinent that existed
about 200 mya.
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TYPES OF PLATE BOUNDARIES

• There are 3 main types of plate boundaries
• Divergent Boundary,
• Convergent Boundary, and
• Transform Boundary

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Divergent Boundary
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Divergent Boundary

• Plates are moving apart
• Occurs at Mid-ocean Ridges and at Rift Valleys
  (seafloor spreading)
• Rift valley deep valleys at the center of a
  mid-ocean ridge.
• Volcanic activity (underwater) and earthquakes
  take place along this boundary.
• Hot springs also come up from hydrothermal vents
  on the ocean floor.

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Divergent Boundary

• Mid-Atlantic Ridge (Atlantic Ocean)

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Divergent Boundary

• East Pacific Rise (Pacific Ocean)

• Transform faults run along the mid-ocean ridges

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Convergent Boundary

• Plates are moving toward each other.
• 2 Types of Convergent Boundaries
• Subduction
• Collision

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Convergent Boundary

• Subduction occurs at
• ocean to ocean plate moving toward each other
• Ocean to continental plates moving toward each
  other
• Oceanic crust is denser than continental crust,
  so oceanic crust will subduct underneath the
  continental plate
• Deep sea trenches are formed
• Volcanic island arcs are formed
• Earthquakes occur

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Convergent Boundary - Subduction

• Islands of Indonesia (ocean to ocean)
• Mariana Islands (ocean to ocean)
• Mariana Trench (Pacific plate moving underneath
  the Philippine Plate)

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Convergent Boundary - Subduction

• Mariana Islands
• Philippine and Pacific plates colliding (ocean to
  ocean)

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Convergent Boundary

• Collision Boundary occurs at
• Continental to continental plate moving towards
  each other
• Builds high mountain chains
• Earthquakes occur along these boundaries

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Convergent Boundary - Collision
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Convergent Boundary - Collision

• Our Appalachian Mountains were also formed this
  way long ago, but are not currently being formed.
  (rounded mountain tops been weathered and
  eroded down)

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Convergent Boundary - Collision

• Himalaya Mountains (sharp and jagged peaks)

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Transform Boundary

• 2 plates are sliding past each other.
• Earthquake activity occurs here

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Transform Boundary

• San Andreas Fault (in California)
• Movement isnt the same along all parts of the
  fault. Some parts can move up to 5cm/yr, while
  others havent moved in over a century.
• North Anatolian Fault (in Turkey)
• Fracture zones along mid-ocean ridges