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PLATE TECTONICS
chapter 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 plategranite, 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 WEGENER
Father of Plate Tectonics
1880-1930
 Studied
Greenland’s
weather
 meteorologist
EVIDENCE FOR “CONTINENTAL
DRIFT”
Shapes of continents
Identical fossils separated by
oceans
glacial deposits in tropics
Mt. 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?