Structural study of the southern Perth Basin by geophysical methods

Abstract

Seismic, gravity and geothermal data were interpreted to examine the structure and the evolution of the southern Perth Basin. Seismic data show that the principal fault trend is north-south and that strike-slip faulting is of major importance in the formation of the basin. Gravity modelling shows that: (a) crustal thickness of the basin is approximately 30 km; (b) greater crustal thickness beneath the basin than on either side implies isostatic imbalance; (c) the Darling and Busselton Faults are steeply dipping faults which extend into the lower crust and control the structure of the southern Perth Basin. Analysis of these data shows that the evolution of the basin has had three major periods of tectonism which reactivated major faults: (a) a right-lateral strike-slip motion along the Darling Fault in the Late Permian-Early Triassic; (b) a phase of tectonism with associated left-lateral motion along the Dunsborough Fault in the Jurassic; (c) the separation of Australia from India in the Early Cretaceous which produced a predominantly tensional, and some oblique-transcurrent, style of faulting.