Structure of the eastern margin of the Perth Basin, Western Australia

Abstract

Deep (12 s TWT) and conventional (6 s TWT) seismic reflection data across the Phanerozoic Perth Basin and adjacent areas of the Precambrian Yilgarn Craton have been interpreted to shed new light on the nature of both the proto-Darling Fault and the basin-bounding Darling Fault. The seismic data, supplemented by gravity modelling, show the proto-Darling Fault to be a sub-vertical feature separating crustal blocks with fundamentally different structures. This is in agreement with geological evidence that shows the crust on either side of the proto-Fault to be of significantly different age. Structural geological evidence suggests the proto-Fault was the locus of significant strike-slip movements. These data collectively support an interpretation of the proto-Darling Fault as a strike-slip suture zone which marks the boundary between two ancient plates/terranes. The Darling Fault is well defined by the seismic data. At New Norcia the fault, based on the structure of its hangingwall sediments, is listric. In contrast, at Moora about 30 km further north, the fault is most likely concave downwards. The difference in structure is probably a function of the geometry of Precambrian strike-slip structures reactivated during Phanerozoic extensional and strike-slip events associated with basin formatiion.