The Theory of Tectonic Plates

1
The Theory of Tectonic Plates

• Chapter 7 Section 3

2
The Theory of Plate Tectonics

• The Earths lithosphere (crust and upper mantle)
  is divided into tectonic plates.
• These plates move on top of the asthenosphere
  (lower mantle).
• We know that these plates move in different ways.

3
Tectonic Plates
4
Tectonic Plate Boundaries

• A boundary is a place where tectonic plates
  touch.
• There are 3 types of tectonic plate boundaries
• Convergent
• Divergent
• Transform

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The numbers on the map represent the rate at
which plates are moving in centimeters.
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Plate Movement
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Convergent Boundary

• When two plates collide, or move toward each
  other, the boundary is called convergent
• There are 3 types of convergent boundaries,
  depending on what type of crust comes together.
• Continental-continental
• Continental-oceanic
• Oceanic-oceanic

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Convergent BoundaryContinental-Continental

• The two continental plates
• come together
• Buckle
• Thicken
• Push continental
• crust upward

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Convergent BoundaryContinental-Oceanic

• Dense oceanic crust sinks below the continental
  crust and sinks into the asthenosphere.
• This is a subduction zone.
• Sub means below (submarine, subway)
• Old ocean crust is pushed below the
  asthenosphere and gets re-melted and recycled.

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Convergent BoundaryOceanic-Oceanic

• One oceanic plate sinks below the other.
• Another subduction zone

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Divergent Boundary

• Two tectonic plates move away from each other.
• On the sea floor at the mid ocean ridge this is
  called sea floor spreading.
• As the plates move apart, magma rises to fill the
  gaps.
• The magma is cooled and forms new ocean floor.

The volcanic country of Iceland, which straddles
the Mid-Atlantic Ridge, offers scientists a
natural laboratory for studying on land the
processes also occurring along the submerged
parts of a spreading ridge. Iceland is splitting
along the spreading center between the North
American and Eurasian Plates, as North America
moves westward relative to Eurasia.
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Divergent Boundary
Sea Floor Spreading
On-land exposure of the Mid-Atlantic Ridge in
Iceland.
13
Transform Boundary

• Two tectonic plates move past one another.
• Their edges are jagged and irregular.
• As they grind together and jerk, they slide past
  each other creating earthquakes.

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Possible Causes of Plate Movement

• Convection Currents hot rock deep in the Earth
  rises, cooler rock sinks. This movement of magma
  causes plates to move
• Ridge push
• Slab pull

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Tracking Tectonic Plate Movement

• Plates move very slowly, centimeters to inches a
  year.
• GPS, Global Positioning System, measures the rate
  of movement.
• Radio signals beam continuously from satellites
  to the Earth.
• By recording the time it takes for the Ground
  station to move a given distance, scientists can
  measure the speed at which plates move.
• Plate Boundary Animation
• http//www.classzone.com/books/earth_science/terc/
  content/visualizations/es0804/es0804page01.cfm?cha
  pter_novisualization
• http//www.wwnorton.com/college/geo/egeo/animation
  s/ch2.htm