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PLATE TECTONICSchapter 7
Interior of Earth
Core– Inner
• Solid Fe; under pressure
– Outer• Liquid Fe
Mantle– Solid; plastic
Crust– Solid; brittle– Si, O2
Plates
Lithosphere- rigid Asthenosphere- rock
that flows
Ocean plate- basalt, dense, thin
Continental plate- granite, less dense, thick
What is a plate?
How do we know what is inside the earth?
core
Outer- no S waves; liquid Magnetic field flip supports liquid outer core Overall density based on orbit Magnetic field= iron
Mantle
Tomography- look at how temp. differs
Volcanoes give us a “peek”
Crust
Directly sample (drill cores)
Sonograms (sound waves)
What moves the plates?
Convection currents
ALFRED WEGENERFather of Plate Tectonics
1880-1930
Studied Greenland’s weather
meteorologist
EVIDENCE FOR “CONTINENTAL DRIFT”
Shapes of continentsIdentical fossils separated by
oceansglacial deposits in tropicsMt. ranges with exact geology
separated by oceans
EVIDENCE FOR “CONTINENTAL DRIFT”
Shapes of continents
Same rock layers match across continents
Ancient climates
No one believed him- why not?
Didn’t know what moved the plates – (still questionable)
Didn’t know where the edge of plates were
Last photo of Wegner Died lost in
Greenland- 1930
NEW EVIDENCE Sonar (1960’s)-
mapped ocean floor
– age of ocean floor is young
– Mirror images of ages on each side of ridges
More “new” evidence
Pattern of earthquakes- outline edges of plates
Maybe Wegner was right!
“New” theory (1968) called
PLATE TECTONIC THEORY
Included:– “new” way plates
move
– “new” ocean evidence
Plate tectonics explains so much!
Location of…– Volcanoes– Earthquakes– Igneous rocks– Metamorphic rocks– Mountains– Folds and faults
PLATE BOUNDARIES
Where plates meet
DIVERGENT
Move apart rifts most under the sea- Mid Ocean Ridge, Red
Sea some continental- East African rift
Divergent boundaries
Fissure eruption
CONVERGENT BOUNDARIES
Move together
Ocean-ocean
Volcanoes form on ocean floor- create island arcs (volcanoes off coast)
trenches
Japan
Ocean-continental (subduction)
trenches composite volcanoes Volcanoes form on
continent
Mt. St. Helens
Continental-continental
Folded mountains- non-volcanic!
Himalayas
Mt. Everest
TRANSFORM(strike-slip)
Plates slide past each other shallow earthquakes
San Andreas Fault
What moves the plates?
Convection currents
Who gives a schist?
Predict earthquake areas Source for geothermal energy Find areas of mineral resources Predict future?