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Download PowerPoint Presentation - Normal Faults
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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 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 Domino block rotation in the Basin and Range Listric (curved) Faults- roll over anticlines Small roll-overs Sedimentation during faulting Growth faulting Animation by R. Allmendinger http://www.geo.cornell.edu/geology/faculty/RWA/movies/ 0 3 km Curved faults – Block rotation Growth Strata Gulf of Mexico Passive Margin Gulf of Mexico Salt Extension Above Salt Diapir Transfer zone in a rift Successive generations of normal faults •Older faults rotate and become inactive •New faults cross-cut them •Result= large magnitude extension
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