Plate Tectonics

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Plate Tectonics
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Alfred Wegener

• 1915- Wegener proposes his hypothesis of
  continental drift.
• Not widely accepted because he could not explain
  WHY?
• Died in 1930 still trying to figure it out.

Continental Drift - 240 million years ago there
was one supercontinent called Pangaea. Over time
the continents have moved to their present
locations and continue to move.
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Evidence-Jigsaw Puzzle Pieces

• South America and Africa fit together.

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Fossil Evidence

• Mesosaurus and Glossopteris
• - Matching fossils found in patterns across
  different continents

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Climatic Evidence

• Glaciers and Coal Deposits
• Signs of glaciers on multiple continents, some
  near equator.
• Found in cold areas but need tropical climate to
  form.

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Rock Evidence

• Age, Type, and Alignment of Mountains
• Appalachian Mtns. Same age and type as mtns. in
  Greenland and Europe

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Plate Tectonics

• Move slowly about 5 cm or 2.5 per year
• Plate movement causes EQs, volcanoes, create
  mountains

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Earths Interior

• Lithosphere plates
• outer and rigid
• Crust and upper mantle
• Moves over the asthenosphere
• Asthenosphere
• below and plastic like
• Lower mantle

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Boundary Types

• Transform
• Plates slide past one another
• Stress involved is shearing
• Forms Eqs
• Ex San Andreas Fault

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Boundary Types

• Divergent
• Plates move away from each other
• Stress involved is tension
• Forms mid ocean ridges and rift zones
• Ex Mid-Atlantic Ridge and Iceland

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• Convergent
• Plates move towards each other
• Stress involved is compression
• 3 different results!

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Boundary Types

• oceanic-continental crusts meet
• Subduction (denser plate oceanic dives below)
• Ocean trench forms offshore
• Continental volcanic arcs
• Ex Cascades, Andes

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Boundary Types

• Oceanic-oceanic crusts meet
• Subduction occurs and one plate dives down
• Ocean trench forms
• Volcanic island arcs
• Ex Japan, Aleutians

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• C) Continental-continental crusts meet
• No subduction
• Collision boundary
• Mountains form
• Ex Appalachians, Himalayas

• Boundary Types

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Plate Tectonic Evidence

• 1. Paleomagnetism
• Polar wandering Polar reversals
• 2. Earthquake patterns
• Earthquakes occur _at_ plate boundaries
• 3. Ocean Drilling
• Glomar Challenger Harry Hess
• 180 million (oceanic) vs. 4 billion (continental)
• 4. Hot spotsexample Hawaii
• Only one active volcano
• Evidence of movement direction
• Islands further from hot spot are oldest

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Causes of Plate Motion

• Scientists generally agree that convection in the
  mantle is the basic driving force for plate
  movement.
• The unequal heating within the earth causes this.
• Read about slab-pull ridge-push.
• Read about mantle convection.