Early Permian East Australian Rift System

Abstract

The Early Permian to Middle Triassic Bowen and Gunnedah Basins in eastern Australia developed in response to a series of interplate and intraplate tectonic events that occurred to the east of the basin system. The initial event was extensional and stretched the continental crust to form part of the major Early Permian East Australian Rift System that occurred at least from far-north Queensland to southern New South Wales. The most important of the rift-related features, in a commercial sense, are a series of half-grabens that form the Denison Trough, now the site of several producing gasfields. The eastern part of the rift system commenced at about 305 Ma and was volcanic dominated. In contrast, the half-grabens in, and to the west of, the Bowen Basin were non-volcanic, and appear to have initiated significantly later, at about 285 Ma. These half-grabens are essentially north–south in length with an extension direction of approximately east-northeast. Mechanical extension appears to have ceased at about 280 Ma, when subsidence became driven by thermal relaxation of the lithosphere. The extension occurred in a backarc setting, in response to far-field stresses that propagated from the west-dipping subduction system at the convergent plate margin of East Gondwanaland that was located to the east of the East Australian Rift System.

Key Words:

• Bowen Basin
• East Australian Rift System
• extension
• Gunnedah Basin
• Permian
• rift system

Acknowledgements

We wish to thank the other members of the Sedimentary Basins of Eastern Australia project from the Geological Survey of Queensland, Geological Survey of New South Wales and Geoscience Australia, in particular Albert Brakel, Allan Wells, Kinta Hoffmann and Peter Green, for many useful discussions during the project, and Joe Mifsud and Veronika Galinec for drafting the figures. We also wish to thank Santos Ltd and MIM Holdings Ltd for providing access to seismic data prior to the data becoming open file. We thank Peter Cawood, Robert Langford and Cameron Marsh for their constructive comments on the manuscript. Published with the permission of the Chief Executive Officer, Geoscience Australia.