Plate Tectonics

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Plate Tectonics
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Brief Structure of the Earth

• Divided into layers
• Core, mantle, crust

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Brief Structure of the Earth

• Lithosphere
• Crust and upper part of the mantle
• About 100 km thick
• Rigid
• Asthenosphere
• Plastic (gooey) layer beneath the lithosphere
• More dense than the lithosphere

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Brief Structure of the Earth

• Continental Crust
• Made up of continents and edges of the oceans
• Light
• Oceanic Crust
• Made up of ocean floor
• More dense than continental crust
• Older oceanic crust is more dense than younger
  oceanic crust

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Theory of Plate Tectonics

• Developed in 1960s
• Combined continental drift and seafloor
  spreading.

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Theory of Plate Tectonics

• Stated that
• The crust and upper mantle (lithosphere) of the
  earth are broken into sections called plates.
• These plates sit on top of the plastic (gooey)
  part of the mantle (asthenosphere).
• These plates can move apart, converge, or slide
  past one another through time.

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Divergent Boundaries

• Where plates are moving apart and new crust is
  forming.
• Example Mid-ocean ridges

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Convergent Boundaries

• Where two plates collide and crust is destroyed.
• Subduction zone
• Area where a dense oceanic plate sinks under a
  light continental plate or another less dense
  oceanic plate
• Forms volcanoes.
• When two continental plates collide high
  mountains are formed.

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Transform Boundary

• Where one plate is sliding past another plate.
• The plates may be going in opposite directions or
  the same direction at different rates.
• Earthquakes are common

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Modern Theories for Cause of Plate Tectonics

• All include convection currents in the mantle.

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Convection Current

• Cycle of heating, rising, cooling, sinking
• Caused by differences in density due to
  differences in temperature
• Example boiling pan of water

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Forces

• Movement of plates result in three types of
  forces
• Tension pulls rocks apart
• Compression pushes rocks together
• Shearing pushes rocks past each other

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Fault

• Surface where rock has broken apart and moved.
• 3 types
• Normal fault
• Reverse fault
• Transform (or strike-slip) fault

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Faults

• Normal fault
• Rock above the fault moves down.
• Formed by tension.
• Reverse fault
• Rock above the fault plane moves up.
• Formed by compression.
• Transform fault
• Bodies of rock slide past each other.
• Formed by shearing.

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Features of Tension Forces

• Mid-ocean ridge
• Where oceanic crust is being pulled apart.
• Rift Valley
• Where continental crust is being pulled apart.

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Features of Compression Forces

• Mountains
• Continental-continental collisions
• Very high mountains (folded mountains) are
  formed.
• Oceanic-continental collisions
• Volcanic mountains are formed.
• Oceanic-oceanic collisions
• Island arcs (volcanoes that reach above the
  surface of the ocean) are formed.

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Features of Shearing

• Earthquakes
• Rocks on each side of a strike-slip fault become
  stuck in one place for a time and then move,
  releasing energy in the form of an earthquake.

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Tracking Plate Movement

• Plate movement is tracked using satellites and
  lasers.
• Current rates of movement range from about 1 cm
  to about 12 cm per year.