Plate Tectonics

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Chapter 9
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Earths Interior Structure
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• Continental Drift hypothesis
• Alfred Wegener
• Supercontinent Pangaea began to break apart 200
  million years ago
• Continents drifted to where they are today

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Breakup of Pangaea
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"Pangea Ultima" is hypothesized to form 250
million years in the Future
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Continental Drift
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Evidence of Continental Drift

• Continental Puzzle
• Fossil
• Geological
• Climate

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Continental Puzzle
Figure 1 A Curious Fit This map shows the best
fit of South America and Africa at a depth of
about 900 meters. The areas where continents
overlap appear in brown. Inferring Why are there
areas of overlap?
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Fossil
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Identical fossil remains of Mesosaurus, a small,
extinct land reptile that lived 270 million years
ago, has been found in both eastern South America
and western Africa. These reptiles could not
have swum across the Atlantic Ocean.
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Geological
Matching Mountain Ranges
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Geological
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Climate
Ancient Glaciers grooves (shown by arrows) in
present day structures)
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Gondwana Reconstruction of Southern hemisphere
super continent. Notice how ring of glaciers
match the patterns of a polar ice
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Glacier Evidence
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• Theory of Plate Tectonics
• Earths crust consists of a number of rigid, but
  moving pieces called plates
• -plates are not defined by continental boundaries

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Lithosphere

• The outer shell of the Earth
• Made of crust and upper mantle
• Rigid but broken into plates that move with
  respect to one another

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Types of Earths Crust

• Oceanic Crust
• Made up of material on the ocean floor

• Continental Crust
• Made up of continental landmasses

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Asthenosphere

• Layer within mantle that lithospheric plates rest
  on
• Molten

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• Convection Currents
• movement of heat through the asthenosphere
• -causes plates to move

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Where convection currents are rising

• New material moves to Earths surface
• Pushes older material aside
• Lithospheric plates move apart

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Where cooler, denser currents are sinking

• Lithospheric plates are pulled together!

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Plate Boundaries

• Place where one plate is moving relative to
  another plate

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Kinds of Plate Boundaries
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Divergent boundaries

• lithospheric plates are moving apart
• Form mid-ocean ridges which have deep valleys
  along entire length called rift valleys
• Seafloor spreading As plates move apart, molten
  rock rises and fills space between plates cools
  and hardens as new ocean floor

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continental rift when a divergent boundary
occurs in a continental landmass creates rift
valley
Continental rift near Krafla, Iceland
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East African Rift Valley
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Transform Fault Boundaries

• Lithospheric plates are sliding past one another
• Transform fault break or crack in the Earths
  crust along which movements have occurred

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Example San Andreas Fault
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Convergent Boundaries

• Lithospheric plates come together
• There are 3 types.

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Oceanic-Continental Convergence

• oceanic plate and continental plate collide
  SUBDUCTION!
• Ocean plate slides under continental plate
  WHY!?!
• Forms deep-ocean trenches and continental
  volcanic arcs

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Continental - Continental Convergence

• Two continental plates collide
• Become crumpled and uplifted
• Form mountain ranges

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Collision of India and Asia
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OCEANIC-OCEANIC Convergence

• One plate is subducted, forms trench
• Subducted plate melts
• Molten rock rises to surface along trench
• Forms island chain called an ISLAND ARC
  (VOLCANOES)

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Evidence of Plate Tectonics

• Paleomagnetism
• Seafloor Spreading
• Earthquake Patterns
• Ocean Drilling
• Hot Spots

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? Paleomagnetism rocks formed millions of years
ago show the location of the magnetic poles at
the time of their formation.

• Normal polaritywhen rocks show the same
  magnetism as the present magnetism field

• Reverse polaritywhen rocks show the opposite
  magnetism as the present magnetism field

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Paleomagnetism Preserved in Lava Flows
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Polarity of the Ocean Crust
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Ocean Drilling

• Confirm seafloor spreading
• Compare age of sediment to distance from
  mid-ocean ridge

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Hot Spots

• Rising plume of mantle pushed towards surface
• Melts and creates a volcanic area
• NOT along plate boundary
• Ex. Hawaiian Islands

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Lets go to this website and review!
CLICK HEREgtgtgt
http//www.pbs.org/wgbh/aso/tryit/tectonics/
Click on Plate Tectonics Activity (with a yellow
arrow) when you get there!
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Here it is all in one big picture
Can you pick out the types of Plate Boundaries?
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Were you right?