handout - university of california, santa cruzpkoch/eart_110a/lectures/... · 2009. 11. 17. · ca...
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Plate boundaries and rates
handout
Plate rates
Plate rates
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Plate rates
Fracture zonesOld ridge orientation~40 Ma
New ridge orientation~28 Ma, rapid change
North Atlantic Spreading Jumped to Iceland Hotspot
N. Am. Grld Europe
N. Am. Grld Europe
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Driving forces
Plate rates
No strong relationship between plate size and rate.Suggests asthenospheric push/drag is not very important.
Area forces are weak drivers
Plate rates
No strong relationship between ridge length and rate.Suggests Ridge Push is not very important.
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Strong positive relationship between circumference of plateas subduction zone and rate. Negative buoyancy is important.
Plate rates - Edge forces
Rate Handout
Pacific fast. Lots of trenchIndia fast. Still responding to subducted ocean
Plate rates
Strong negative relationship between continental area ofplate and rate.
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Continents are slow. WhyDeep keels (drag) or lack of trenches ?
Summary85% of the driving force of plate tectonics is slabsubduction (negative buoyancy).10% of the driving force is trench pull (coming up).5% other forces
The cooling effect associated with ridge systems is thekey factor responsible for plate tectonics.
Subduction Angle
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Subduction Angle
Trench suction
Ridge hits trench
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San Andreas Evolution
Slab Window
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