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Geol341 Outline Ch. 17 • Extensional Environments • Shape of normal faults –Planar – Listric – Roll-over • Block rotation Normal Faults • Growth faults • Detachment surfaces Extensional • Movie • Analog models

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

Extensional Tectonics Continental Tectonic Settings for Extension

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

Oceanic Rift Normal Faults Continental Extension

1 Extension in Convergent Margins Back Arcs Bounded by normal faults

Van der Pluijm and Marshak (2004)

Extension of the 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 , North Sea. (Fossen, 2010)

Map view Gulfaks Pure 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

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 - Large magnitude 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

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