extensional margins intercontinental rift zones spreading centers
TRANSCRIPT
Extensional margins
Intercontinental rift zones
Spreading centers
Spreading Centers
Iceland Oceanic ridges
Gulf of Suez Rift
Intercontinental rifting
Basin and Range
Extensional faults in Canyonlands National Park, Utah
Analog models of extension
Go to movie of our sandbox experiment
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Analog models of extension
Claybox experiments at UMass
Investigations with extension
experiment in progress at UMass with undergraduates
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
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?
Activities
ObserveSketch <-> observeLabelMeasureGraphPredict
Data Collection
# turns (cm) Basin depth (cm)
Basin length (cm)
# active faults
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
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?
Hey what about strike slip?
Clay shows interesting patterns of echelon cracksClay cake on top of two
boardsPull one board slowly
From SERC