The Theory of Plate Tectonics

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The Theory of Plate Tectonics
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Plate Tectonics

• The Earths lithosphere is divided into plates
  that move on top of the asthenosphere.

Earths Major Plates
Lithosphere
Asthenosphere
When the water moves beneath the raft, the raft
moves with it. When the asthenosphere moves, the
lithosphere moves with it
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Types of Plate Boundaries

• When two plates meet, they form a boundary.
• There are three types of boundaries
• Convergent
• Divergent
• Transform

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Convergent Boundaries

• Two plates push together
• Term to know SUBDUCTION means the crust is
  SINKING!
• Three types of convergent boundaries
• 1. Ocean/Ocean TRENCH
• 2. Ocean/Continental TRENCH
• 3. Continental/Continental MOUNTAINS

Oceanic crust sinks, Continental crust rises!!
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Convergent Collision 1 (Oceanic/Oceanic)

• Both oceanic plates SINK (subduction!) and form a
  TRENCH. Magma rises and forms and island arc of
  volcanoes.

Subduction Zone
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Convergent Collision 2 (Oceanic/Continental)

• The oceanic plate sinks (subduction!) below the
  continent and the continental plate slides over
  the top of the oceanic plate. Forms a TRENCH.

Subduction Zone
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Convergent Collision 3(Continental/Continental)

• Both continental plates collide and rise up
  forming MOUNTAINS. (Ex. Himilayas)

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Divergent Boundaries

• Two plates pull apart causing a rift valley in
  the middle.
• Sea-floor spreading is created by a divergent
  boundary.

Rift Valley
Mid Ocean Ridge
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Transform Boundaries

• Plates slide past each other in a side to side
  motion. (Ex. San Andreas Fault)

This fence used to line up!!
San Andreas Fault
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WHY do the plates move?

• CONVECTION CURRENTS in the mantleHot rock
  (less dense) rises to the surface, cools (more
  dense), and sinks back to the mantle.

COOL ROCK SINKS
HOT ROCK RISES
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Convection Currents