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
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