Geol341-342 Outline Ch. 16 • Extensional Environments • Shape of normal faults Normal Faults –Planar – Listric Extensional Tectonics – Roll-over anticlines • 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, rifts 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 Fault –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 rift 5.