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Normal Faults Extensional Tectonics Geol341 Outline Ch. 17 • Extensional Environments • Shape of normal faults –Planar – Listric – Roll-over anticlines • Block rotation Normal Faults • Growth faults • Detachment surfaces Extensional Tectonics • Movie • Analog models Many diagrams are from Earth Structure, van der Pluijm and Marshak, 2004 2016 Extensional Tectonics Continental Rift Tectonic Settings for Extension • Divergent plate motions • Gravitational collapse – Over-thickened crust – Continental margins • Salt Domes Oceanic Rift Normal Faults Continental Extension 1 Extension in Convergent Margins Back Arcs Rifts Bounded by normal faults Van der Pluijm and Marshak (2004) Extension of the lithosphere 1 1300oC Van der Pluijm and Marshak (2004) Extension of the lithosphere 2 Consequences of Lithospheric Extension •Thinning of the lithosphere •Normal faulting at the surface •High heat flow (rinsing of the isotherms) 1300oC •Thermal subsidence during cooling after end of extension- > sedimentary basins Van der Pluijm and Marshak (2004) 2 North Sea Extensional Basin Evolution Norway Basin Depth to basement contour map Present Day North Sea Basin Scotland Fossen, 2010 3D view Gulfaks Field, North Sea Norway Structure of the base Cretaceous, east Viking graben, North Sea. (Fossen, 2010) Map view Gulfaks Pure shear vs. simple shear systems North Se Van der Pluijm and Marshak (2004) Fossen, 2010 3 Gravitational Collapse of Mt. Basin and Belts Range Province Weak Van der Pluijm and Marshak (2004) New Mountains-Active Fault –Basin and Range Province Deep seismic reflection data from extensional system Two modes of extension (Basin and Range) Van der Pluijm and Marshak (2004) 4 Geometry of Extensional Belts Parsons, 2010 Block Rotation Sandbox- Block rotation Sand above plasticine Van der Pluijm and Marshak (2004) Domino block rotation in the Basin and Range Successive generations of normal faults •Older faults rotate and become inactive •New faults cross-cut them •Result= large magnitude extension 5 Listric Normal Faults Listric (curved) Faults- roll over anticlines Small roll-overs Sedimentation during faulting Curved faults – Block rotation Growth Strata Growth faulting 0 3 km Animation by R. Allmendinger http://www.geo.cornell.edu/geology/faculty/RWA/movies/ 6 Hammerfest Basin, Norway NW SE Gulf of Mexico CI = 300 m 50 km Passive Continental Margin Gulf of Mexico Extension Above Salt Diapir Salt 7 Metamorphic Core Complex- Large magnitude Transfer zone in a rift extension Take home points • Normal faults form in divergent plate boundaries, areas of gravitational collapse and extension above salt domes • Also, back-arc rifts form convergent plate boundaries • Thinning and cooling of the lithosphere after continental rifting creates basins • The basin and range is an example of gravitational collapse of a contractional orogen. • Series of normal faults rotate like books on a shelf • Curved normal faults (listric) produce roll-over anticlines • Sedimentary deposits are thick and tilted like a fan on the hanging wall of listric normal faults • Continental passive margins are full of down to the basin normal faults and often salt layers 8.
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  • Part 3: Normal Faults and Extensional Tectonics
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