Magnetotelluric Surveys Across Major Precambrian Tectonic Boundaries in Southern Western Australia

Magnetotelluric data have been recorded along two traverses in southern Western Australia. The survey locations were chosen so as to define conductivity structure in the deep crust and upper mantle across fundamental geological boundaries within and at the margin of the Yilgarn Craton. Data across the suture zone between the Archean Yilgarn Craton and the adjacent Proterozoic Albany-Fraser Orogen suggest major structures and crustal blocks have been successfully mapped based on their conductivity characteristics. The data are interpreted as showing the orogen is largely allochthonous and the suture zone may contain remanent oceanic crust and suspect terranes of continental affinity. Preliminary results from a survey across the southern Yilgarn Craton from the Southern Cross to Eastern Goldfields greenstone terrains suggest major fault structures, such as the Koolyanobbing shear zone, extend in to the deep crust and dip to the east. A zone of anomalously conductive mantle occurs beneath the Lake Johnston greenstone belt. This belt contains nickel sulphide deposits but the origin and significance of the mantle feature and any link to the mineralisation remains equivocal.