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Normal Faults Extensional Tectonics - West Virginia …pages.geo.wvu.edu/~jtoro/structure/ppt/12NormalFaults.pdf · Normal Faults Extensional Tectonics Geol341 Many diagrams are from

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    Normal FaultsExtensional Tectonics

    Geol341

    2016Many diagrams are from Earth Structure, van der Pluijm and Marshak, 2004

    OutlineCh. 17

    Extensional Environments Shape of normal faults

    Planar Listric Roll-over anticlines

    Block rotation Growth faults Detachment surfaces Movie Analog models

    Tectonic Settings for Extension

    Divergent plate motions Gravitational collapse

    Over-thickened crust Continental margins

    Salt Domes

    Extensional TectonicsContinental Rift

    Oceanic RiftNormal Faults Continental

    Extension

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    Rifts

    Bounded by normal faults

    Extension in Convergent MarginsBack Arcs

    Van der Pluijm and Marshak (2004)

    Extension of the lithosphere 1

    Van der Pluijm and Marshak (2004)

    1300oC

    Extension of the lithosphere 2

    Van der Pluijm and Marshak (2004)

    1300oC

    Consequences of Lithospheric Extension

    Thinning of the lithosphere

    Normal faulting at the surface

    High heat flow (rinsing of the isotherms)

    Thermal subsidence during cooling after end of extension- > sedimentary basins

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    North Sea Basin

    Depth to basement

    contour map

    Norway

    Scotland

    Extensional Basin Evolution

    Present Day North Sea Basin

    Fossen, 2010

    Structure of the base Cretaceous, east Viking graben, North Sea. (Fossen, 2010)

    Norway

    3D view Gulfaks Field, North Sea

    Map viewGulfaks North Se

    Pure shear vs. simple shear systems

    Van der Pluijm and Marshak (2004)

    Fossen, 2010

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    Gravitational Collapse of Mt. Belts

    Van der Pluijm and Marshak (2004)

    Weak

    Basin and Range

    Province

    New Mountains-Active Fault Basin and Range Province

    Two modes of extension

    Van der Pluijm and Marshak (2004)

    Deep seismic reflection data from extensional system(Basin and Range)

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    Parsons, 2010

    Geometry of Extensional Belts

    Sandbox- Block rotation

    Sand above plasticine

    Block Rotation

    Van der Pluijm and Marshak (2004)

    Domino block rotation in the Basin and Range

    Older faults rotate and become inactiveNew faults cross-cut themResult= large magnitude extension

    Successive generations of normal faults

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    Listric Normal Faults Listric (curved) Faults- roll over anticlines

    Small roll-overs

    Sedimentation during faultingGrowth faulting

    Animation by R. Allmendinger http://www.geo.cornell.edu/geology/faculty/RWA/movies/

    Curved faults Block rotationGrowth Strata

    3 km

    0

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    NW SE

    Hammerfest Basin, Norway

    50 kmCI = 300 m

    Gulf of Mexico

    Passive Continental Margin

    Gulf of Mexico

    SaltExtension Above Salt Diapir

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    Transfer zone in a riftMetamorphic Core Complex- Large magnitude 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