Extensional margins Intercontinental rift zones Spreading centers.
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Transcript of Extensional margins Intercontinental rift zones Spreading centers.
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Extensional margins
Intercontinental rift zones
Spreading centers
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Spreading Centers
Iceland Oceanic ridges
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Gulf of Suez Rift
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Intercontinental rifting
Basin and Range
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Extensional faults in Canyonlands National Park, Utah
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Analog models of extension
Go to movie of our sandbox experiment
QuickTime™ and aCinepak decompressor
are needed to see this picture.
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Analog models of extension
Claybox experiments at UMass
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Investigations with extension
experiment in progress at UMass with undergraduates
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Aims of the investigation:
Does the Earth’s crust deform under extension the same as under contraction?
Is the pattern of earthquakes the same in extension and contraction?
Wasatch Mountains in Utah
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Questions of investigation:
How does topography change during extension?
What causes the topography to change?Where are the active
faults located?How many faults are
active at any time?
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Activities
ObserveSketch <-> observeLabelMeasureGraphPredict
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Data Collection
# turns (cm) Basin depth (cm)
Basin length (cm)
# active faults
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Extensional faults dip different from contraction
Shallow faults form during contraction (30˚ dip)Steep faults form during extension (60˚ dip)It is consistent!
Extension and contraction are 90˚ apart
6030
3060
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Effect of Existing faults
Cut a fault into the sand pack that might not be oriented as favorably for slip as a new fault.Does the new fault form or
old fault reactivate?
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Hey what about strike slip?
Clay shows interesting patterns of echelon cracksClay cake on top of two
boardsPull one board slowly
From SERC