Salt diapir reactivation and normal faulting in an oblique extensional system, Vulcan Sub-basin, NW Australia

Abstract

Oblique extension and salt diapirism have their own distinct mechanisms that control the geometry and kinematics of structures. In this study, we document a geological phenomenon from the Vulcan Sub-basin in NW Australia that combines these processes: a salt diapir reactivated in an oblique extensional system. Detailed structural analysis of this natural example, with a focus on normal fault systems, allows characterization of the oblique extensional system and investigation of how the pre-existing structural fabrics and salt diapir control deformation, and interact with each other under oblique extension. After comparison with forward modelling results and using constraints from geological evidence, our fault strike analysis indicates that the Neogene flexural extension orientation in the oblique extensional system is around 347°, revealing a perpendicular relationship between extension direction and fault strikes from the deformation zone. The salt diapir, reactivated during Neogene extension, strongly influences local structure in the oblique extensional system by altering fault strikes, stepping patterns, deformation zone width and fault density, indicative of a ‘stress–strain concentration’ effect of the salt diapir owing to its extremely low strength. These results provide valuable insights into the understanding of oblique extensional systems, the geomechanical role of salt during extension, and the Neogene tectonic evolution of NW Australia. Supplementary material : Dominant seismic frequency analysis, uninterpreted seismic profiles, additional structural and isochron maps, a 3D view of fault systems, and original measurements of the fault system are available at http://doi.org/10.6084/m9.figshare.c.3148321.