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Plate TectonicsAlfred Wegener 1915 Continental Drift
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Pangaea
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QuickTime™ and aCinepak decompressor
are needed to see this picture.
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Sonar
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Atlantic Ocean
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World Ocean Floor
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Magnetic Field
Magnetic north is several degrees off geographic north, and it alsowanders around.
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Rocks and magnetism
Fe-rich minerals recordthe direction of ‘north’ aswell as their latitude asthey crystallize.
Basalt, the kind of rock thatmakes up oceanic crust, hasFe-rich minerals.
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Magnetic Reversals
The Earth’s magnetic fieldreverses every so often. Whenthis happens, magnetic northbecomes located near the SouthPole.
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Magnetometer readings show that basaltic rocks have the same readings on either sideof the MOR (mid-oceanic ridge).
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Magma generation at MOR
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
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Basalts are youngest along the MOR, where they are generated, then getprogressively older away from, and on either side of, the MOR.
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Seafloor Spreading
Generation of basalt at mid-oceanic ridge
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Tectonic Plates
3 major types
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Pillow Basalt
Lava extruded in water takes the form of ‘pillows.’
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Divergent Plate Boundaries
MOR is 42,000miles long
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Triple Junction
Initial formation of a divergent plate boundary takes the form of severaltriple junctions.
As spreading continues, one of the rift valleys has to fail: Aulacogen
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East African Rift
Aulacogen
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Mature Divergent Boundary
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3 types of…
3 types of convergent plateboundaries:
1) Oceanic-Continental
2) Oceanic-Oceanic
3) Continental-Continental
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Oceanic-Continental Convergence
Accretionary Wedge
Volcanic arc appears approx. 200 miles inland from the trench.Magma pulses separated by about 400 years.Partial melting creates continental crust (we’ll discuss later).
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Oceanic-Oceanic Convergence
Older, and thus colder & denser, crust subducts.Similar to oceanic-continental convergence, but forms
volcanic island arc.
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Earthquake Distribution Map
Distribution of earthquakes mirrors the tectonic boundaries.
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Benioff Zone
Deeper earthquakes arealways found far inlandof the trench.
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Continental-Continental Convergence
Collision happens after oceanic crust is completelyconsumed during continental-oceanic subduction.
Continental crust is not dense enough to be forceddown into the mantle.
Ocean-bottom sedimentsforced upward.
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Collision
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Himalaya
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India-Asia Collision
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QuickTime™ and aCinepak decompressor
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Trenches
Trenches: Where oceanic crust is subducting
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Transform Plate Boundary
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San Andreas Fault
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SegmentsEach segment moves at a different rate, some not at all
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Earthquake Hazards
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Mantle Plumes
Subducting oceanic crust melts at the core-mantle boundary, releasing lots of magma.Magma rises to the surface over a 600,000 year period.
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Hawaii
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Hawaiian hot spot
Hot spot is fixedPlate moves over hot spot
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Hawaiian Hot Spot
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Hot Spots
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Yellowstone
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Yellowstone
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Fallout
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Earth