Theory of Plate Tectonics

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Plate Tectonics
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What is Plate Tectonics

• The Earths crust and upper mantle are broken
  into sections called plates
• Plates move around on top of the mantle like rafts

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Layers of the Earth

• Crust
• Mantle
• Lithosphere
• Athenosphere
• Inner core
• Solid
• Outer Core
• Liquid

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What is the Lithosphere?

• The crust and part of the upper mantle
  lithosphere
• 100 km thick
• Less dense than the material below it so it
  floats

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What is the Asthenoshere?

• The plastic layer below the lithosphere
  asthenosphere
• The plates of the lithosphere float on the
  asthenosphere

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2 Types of Plates

• Ocean plates - plates below the oceans
• Continental plates - plates below the continents

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Questions...

• What is the theory of plate tectonics?
• What is the lithosphere?
• What is the asthenosphere?
• What is the connection between the two?
• What are the two types of plates?

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Causes of Plate Tectonics
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Convection Currents

• Plates move by the transfer of heat through
  heated material.
• Hot magma in the Earth moves toward the surface,
  cools, then sinks again.
• Creates convection currents beneath the plates
  that cause the plates to move.

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Questions...

• What causes plates to move?
• How is a convection current formed?

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Plate Boundaries
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Major Plate Boundaries

• Earth has 6 major plate boundaries

1. Eurasian
2. Pacific
3. African
4. N. American
5. S. American
6. Antarctic

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Plate Boundary Types
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1. Divergent Boundaries

• Boundary between two plates that are moving apart
  or rifting
• ? ?
• RIFTING causes SEAFLOOR SPREADING
• At the mid-ocean ridge moves 6 cm/year

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Features of Divergent Boundaries

• Mid-ocean ridges
• rift valleys
• fissure volcanoes

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2. Transform Fault Boundaries

• Boundary between two plates that are sliding past
  each other
• Moving in opposite directions
• Moving in same directions at different speeds
• EARTHQUAKES along faults
• Ex San Andreas fault in CA

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San Andreas Fault, CA
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3. Convergent Boundaries

• Boundaries between two plates that are colliding
• ? ?
• There are 3 types

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Type 1

• Ocean plate colliding with a less dense
  continental plate
• Subduction Zone where the more dense plate
  slides under the less dense plate
• VOLCANOES occur at subduction zones
• Earthquakes are common

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Andes Mountains, South America
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Type 2

• Ocean plate colliding with another ocean plate
• The more dense plate slides under the less dense
  plate creating a subduction zone called a TRENCH
• May form volcanoes a.k.a. volcanic island arc

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Aleutian Islands, Alaska
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Type 3

• Two continental plates collide the Continental
  rocks buckle rise
• Have Collision Zones
• a place where folded thrust faulted mountains
  form
• Earthquakes are common
• Little volcanic activity
• Continental motion occurs 1-5 cm/year

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Questions...

• What are the three types of boundaries?
• What direction do plates go for each?
• Which boundary has a subduction zonewhat occurs
  at a subduction zone?

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Alfred Wegener

• In 1915, German geologist Dr. Alfred Wegener
  proposed an idea called the Theory of Continental
  Drift.
• Said all continents were joined together about
  250 million years ago as a supercontinent Pangea
  (all land).
• Eventually Pangea split and moved into current
  positions

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Wegners Clues or Evidence..

• Shape of the continents
• They seem to fit together as one big puzzle.

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Clues or Evidence continued

• Fossil evidence

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Clues or Evidence continued

• Climate (Glacial Deposits)..

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Clues or Evidence continued

• Rocks - similar mountain ranges found on
  different continents separated by oceans

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Evidence

• A system of underwater mountain chains or
  mid-ocean ridges, rise thousands of meters above
  ocean floor
• Caused by plate movement called sea-floor
  spreading at a divergent boundary
• Youngest ocean floor rocks near mid ocean
  ridges
• Oldest near the edge of the continents
• When the sea floor reaches a continental
  boundary, it is forced downward beneath the
  continental, called a sea floor trench