The Theory of Plate Tectonics

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The Theory of Plate Tectonics
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• Canadian scientist, J. Tuzo Wilson noticed the
  continental crusts had cracks similar to oceanic
  crust

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Lithosphere is broken into sections called plates

• Plate tectonics- geologic theory stating that
  pieces of Earths lithosphere are in constant,
  slow motion, driven by convection currents in the
  mantle

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The theory of plate tectonics explains the
formation, movement, subduction of Earths
plates
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• Plates meet at plate boundaries extending deep in
  the lithosphere
• Faults- breaks in Earths crust where rocks slip
  past each other form along boundaries

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3 Types of Plate Boundaries

• Divergent
• Convergent
• Transform

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Transform Boundary

• Crust is neither created nor destroyed
• 2 plates slip past each other moving in opposite
  directions
• Earthquakes occur frequently here

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Divergent Boundary

• Place where 2 plates move apart
• Most found along mid-ocean ridge where oceanic
  crust diverges

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Divergent boundaries also occur on land

• Rift valleys form when continental crust diverges
• Rift may eventually split a continent

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Convergent Boundary

• Place where 2 plates come together, converge
• Collisions may occur between 2 oceanic plates, 2
  continental plates, or an oceanic continental
  plate

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Oceanic-Oceanic Convergence

• Oceanic crust becomes cooler denser as it
  spreads away from the mid-ocean ridge
• 2 oceanic crusts meet at a trench the more
  dense plate subducts under the other plate
  returns to the mantle
• Oceanic convergence creates island arcs

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Oceanic-Continental Convergence

• Oceanic crust, made of basalt, is denser than
  continental crust, made mostly of granite
• Oceanic plate sinks beneath the continental crust

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Continental-Continental Convergence

• Subduction does NOT occur when 2 pieces of
  continental crust collide
• Neither plate is dense enough to sink
• Crust is squeezed into mountain ranges

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Continents Slow Dance

• Plates move at an extremely slow rate, 1-10
  cm/year
• North American European plate are moving apart
  at about the same rate as your finger nails grow

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Tracking Tectonic Plate Motion

• Scientists use data from a system of satellites
  called Global Positioning System (GPS) to measure
  the rate of motion of tectonic plates.

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Review what you know

• 1. Define plate tectonics.
• 2. Describe the three boundaries of plate
  movement.
• 3. How do scientists measure the rate of tectonic
  plate movement?