Deep conductivity anomaly of the Darling Fault Zone ? implications for fluid transport in the Perth Basin

Abstract

The Darling Fault Zone (DFZ) is one of the largest lineaments in the world, mapped over approximately 1000km. It is a long-lived feature with imprints of multiple deformation phases with multiple orientations since the Archean. Although it is still topography forming in some areas, and therefore must have recent activity, its seismic quiescence reduces the perceived need for scientific investigation into the extent and physical properties of this crustal scale fault. Seismic activity is common in the south west of Western Australia and evidence suggests these are located on faults that communicate with the DFZ. It is therefore paramount to have more detailed understanding on the fault architecture and the role of fluids in lubricating aseismic slip. Magnetotelluric (MT) data are acquired along transects across the Perth Basin and the western margin of the Yilgarn Craton providing deep, high resolution data about the electrical structure of the DFZ. In this contribution we focus on the interpretation of the data, details on the acquisition and analysis are presented in the poster session. Using impedance tensor analysis and 2D modelling techniques, we map the DFZ to the base of the crust, confirming it as a lithospheric feature. We reveal a complex pattern of deep-seated conductivity associated with the foot wall of the DFZ that persists to depth. Resistivity models are used to estimate porosity on the DFZ, identifying a more complex internal structure for the DFZ than generally considered, with important implications for fluid transport in the basin.