Download CH 9 Plate tectonics

CH 9 Plate tectonics
• 1915 – Alfred Wegener proposed his
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continental drift hypothesis
200 mya one large super-continent Pangaea
(all lands) began to break up
Panthalassa – all oceans
Not widely accepted b/c he couldn’t explain
why it occurred
Dies in 1930 trying to figure it out
Evidence
• Jig-saw puzzle pieces fit
• SA and Africa
• Fossil evidence
• Mesosaurus and Glossopteris
• Climatic evidence
• Glaciers and coal deposits
• Rock evidence
• Age, type, alignment of mts
Plate Tectonics
• Move slowly about 5 cm or 2.5” per year
• Plate movement causes EQs, volcanoes, mts
• Lithosphere – plates
• outer and rigid
• Crust and upper mantle
• Moves over the asthenosphere
• Asthenosphere
• below and plastic like
• Lower mantle
Boundary Types
1. Transform
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Plates slide past one another
Stress involved is shearing
Forms Eqs
Ex: San Andreas Fault
2. Divergent
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Plates move away from each other
Stress involved is tension
Forms mid ocean ridges and rift zones
Ex: Mid-Atlantic Ridge and Iceland
3. Convergent
• Plates move towards each other
• Stress involved is compression
• 3 different results!
A) oceanic-continental crusts meet
• Subduction (denser plate [oceanic] dives
below)
• Ocean trench forms offshore
• Continental volcanic arcs
• Ex: Cascades, Andes
B) Oceanic-oceanic crusts meet
• Subduction occurs and one plate dives
down
• Ocean trench forms
• Volcanic island arcs
• Ex: Japan, Aleutians
C) Continental-continental crusts meet
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No subduction
Collision boundary
Mountains form
Ex: Appalachians, Himalayas
• Pie crust meets hand tossed)
• Thinner and more sweet
• Holds up better to washings
• Able to leap tall buildings in a single
bound.
• Makes Jessica Alba look like a ho.
Plate Tectonic Evidence
1. Paleomagnetism
• Polar wandering & Polar reversals
2. Earthquake patterns
• Earthquakes occur @ plate boundaries
3. Ocean Drilling
• Glomar Challenger & Harry Hess
• 180 million (oceanic) vs. 4 billion (continental)
4. Hot spots—example = Hawaii
• Only one active volcano
• Evidence of movement & direction
• Islands further from hot spot are oldest
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.