A Hybrid Hard- and Soft-Linked Fault Model for the Development of Australian Extensional Basin Systems: Reconciling Observations from Seismic, Aeromagnetic and Analogue Modelling Data

Geoffrey W. O'Brien, Philip Symonds, Jane Blevin, and Richard Higgins

A series of rift models has been developed for basin systems around Australia, via the interpretation of newly acquired deep crustal seismic and high resolution aeromagnetic data. These models, which incorporate observations on rift architecture, fault geometries, fault orientation, basement fabric/grain, extensional transport direction and reactivation history, have then been iteratively tested by over twenty-five sophisticated analogue modelling experiments.

This work has led to the development of a hybrid hard-linked/soft-linked fault model for the Australian margin. In this model, basement grain is the principal control on the rift architecture that develops, with pre-existing fractures acting to establish discrete offsets (hard-linkages) between adjacent extensional faults and rift segments. It is these basement features which produce the recti-linear features which are so common on aeromagnetic data around the Australian margin. With progressively greater extension, the basement-involved, hard-linked system exerts virtually no influence over the type or intensity of faulting within the syn-rift phase, though they do control the fault location. Syn-rift faulting is dominated by "soft-linked" fault systems, with relay ramps/zones accomm dating jumps in the position of the basin margin faults.

During basin reactivation (particularly inversion), it is the location and geometry of the underpinning, hard-linked basement features which ultimately control the locations of the traps that develop in the syn- and post-rift section, whereas it is the soft-linked fault system which is the primary control on the fluid migration pathways. Reconciling these concepts provides a set of powerful predictive tools for exploring both frontier and mature basins.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California