Balancing sub- and supra-salt strain in salt-influenced rifts: Implications for extension estimates. (September 2017)

• Record Type: Journal Article
• Authors: Coleman, Alexander J.; Jackson, Christopher A.-L.; Duffy, Oliver B.
• Is Part Of: Journal of structural geology. Volume 102(2017:Sep.)
• Page Start: 208
• Page End: 225
• Publication Date: 2017-09
• Subjects: Salt-influenced rifting -- Strain balancing -- Normal faulting -- Halten Terrace -- Extension estimates -- Fault-related folding; Geology, Structural -- Periodicals; Géomorphologie structurale -- Périodiques; Geology, Structural; Periodicals; 551.805
• DOI: 10.1016/j.jsg.2017.08.006
• Languages: English
• ISSNs: 0191-8141

Abstract

Abstract: The structural style of salt-influenced rifts may differ from those formed in predominantly brittle crust. Salt can decouple sub- and supra-salt strain, causing sub-salt faults to be geometrically decoupled from, but kinematically coupled to and responsible for, supra-salt forced folding. Salt-influenced rifts thus contain more folds than their brittle counterparts, an observation often ignored in extension estimates. Fundamental to determining whether sub- and supra-salt structures are kinematically coherent, and the relative contributions of thin- (i.e. gravity-driven) and thick-skinned (i.e. whole-plate stretching) deformation to accommodating rift-related strain, is our ability to measure extension at both structural levels. We here use published physical models of salt-influenced extension to show that line-length estimates yield more accurate values of sub- and supra-salt extension compared to fault-heave, before applying these methods to seismic data from the Halten Terrace, offshore Norway. We show that, given the abundance of ductile deformation in salt-influenced rifts, significant amounts of extension may be ignored, leading to the erroneous interpretations of thin-skinned, gravity-gliding. If a system is kinematically coherent, supra-salt structures can help predict the occurrence and kinematics of sub-salt faults that may be poorly imaged and otherwise poorly constrained. Highlights: Rifts accommodate extension by ductile (folding) and brittle (faulting) strain. Folding is often not included in extension estimates, especially using fault-heave. Models and seismic of salt-influenced rifts show that line-length is more accurate. Fault arrays above and below salt should not be interpreted as isolated systems. Misinterpreting extension may impact tectonic histories and basin models.