Normal Faults Extensional Tectonics

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Normal FaultsExtensional Tectonics
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Tectonic Settings for Extension

• Divergent plate motions
• Gravitational collapse
• Over-thickened crust
• Continental margins
• Salt Domes

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Extensional Tectonics
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Divergent BoundaryNormal Faults, rifts
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Continental Extension
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Divergent Boundaries Continental Plate Separation
Parallel valleys volcanoes and earthquakes.
East African Rift Valley
Somali Subplate
African Plate
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Rifts
Rifts Bounded by normal faults
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Back Arc extension
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Extension of the lithosphere 1
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Extension of the lithosphere 2
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Lithospheric Extension

• Thinning of the lithosphere
• Normal faulting at the surface
• High heat flow (rinsing of the isotherms)
• Thermal subsidence - gt sedimentary basins

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North Sea Extensional Basin
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Pure shear vs. simple shear systems
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Gravitational Collapse of Mt. Belts
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Basin and Range Province
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New Mountains-Active Fault Basin and Range
Province

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Two modes of extension
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Out crop- domino blocks
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Sandbox- Block rotation
Sand above plasticine
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Block Rotation
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Domino block rotation in the Basin and Range
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Listric (curved) Faults- roll over anticlines
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Small roll-overs
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Sedimentation during faultingGrowth faulting
Animation by R. Allmendinger http//www.geo.cornel
l.edu/geology/faculty/RWA/movies/
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Curved faults Block rotationGrowth Strata
0
3 km
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Gulf of Mexico
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Passive Margin
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Gulf of MexicoSalt
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Extension Above Salt Diapir
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Transfer zone in a rift
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Successive generations of normal faults

• Older faults rotate and become inactive
• New faults cross-cut them
• Result large magnitude extension

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