20 extension
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Normal Faults
Extensional Tectonics
Tectonic Settings for Extension
• Divergent plate motions
• Gravitational collapse
– Over-thickened crust
– Continental margins
• Salt Domes
Extensional Tectonics
Divergent Boundary
Normal Faults, rifts
Continental
Extension
Divergent Boundaries
Continental Plate Separation
Parallel valleys; volcanoes and earthquakes.
East African
Rift Valley
a te
l
P
an
c
i
r
f
A
Soma
l i S ub
plate
Rifts
Bounded by
normal faults
Back Arc extension
Extension of the lithosphere 1
Extension of the lithosphere 2
Lithospheric Extension
•Thinning of the lithosphere
•Normal faulting at the surface
•High heat flow (rinsing of the isotherms)
•Thermal subsidence - > sedimentary basins
North Sea Extensional Basin
Pure shear vs. simple shear
systems
Gravitational Collapse of Mt.
Belts
Basin and
Range
Province
New Mountains-Active Fault –Basin and
Range Province
Two modes of extension
Sandbox- Block rotation
Sand above plasticine
Block Rotation
