Geol341-342 Outline Ch. 16 • Extensional Environments • Shape of normal faults Normal Faults –Planar – Listric Extensional – Roll-over • Block rotation • Growth faults • Detachment surfaces • Movie • Analog models

Many diagrams are from Earth Structure, van der Pluijm and Marshak, 2004 2008

Extensional Tectonics Tectonic Settings for Extension

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

Divergent Boundary Normal Faults, Continental Extension

1 Back Arc extension

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 Lithospheric Extension

•Thinning of the lithosphere •Normal faulting at the surface •High heat flow (rinsing of the isotherms) •Thermal subsidence - > sedimentary basins 1300oC

Van der Pluijm and Marshak (2004)

2 North Sea Norway North Sea Extensional Basin Basin

Scotland Van der Pluijm and Marshak (2004)

Gravitational Collapse of Mt. Basin and Belts Range Province

Weak

Van der Pluijm and Marshak (2004)

New Mountains-Active –Basin and Range Province Two modes of extension

Van der Pluijm and Marshak (2004)

3 Block Rotation Sandbox- Block rotation

Sand above plasticine Van der Pluijm and Marshak (2004)

Listric (curved) Faults- roll over Small roll-overs anticlines

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/

4 Gulf of Passive Continental Margin Mexico

Gulf of Mexico Salt

Extension Above Salt Diapir Transfer zone in a

5