Identifying the lithospheric structure of a Precambrian orogen using magnetotellurics: The Capricorn Orogen, Western Australia

Abstract

A 300-km long magnetotelluric (MT) survey was carried out across the Capricorn Orogen in Western Australia. The Capricorn Orogen includes reworked crust of the Archaean Yilgarn and Pilbara Cratons, and the allochthonous latest Archaean to Palaeoproterozoic Glenburgh Terrane in the southern Gascoyne Complex and the Palaeoproterozoic northern Gascoyne Complex. The survey aimed to increase our understanding of the juxtaposition of these crustal elements by obtaining information about their electrical structure with depth. Phase tensor analysis of the data showed that 2D MT inversion could only be carried out for stations in the centre of the profile, crossing the Gascoyne Complex. The resulting model showed that there is no electrical distinction between the Glenburgh Terrane and the northern Gascoyne Complex, suggesting that the Glenburgh Terrane may form basement to the whole of the Gascoyne Complex. 3D forward modelling was carried out for the entire survey line, incorporating the basement blocks as well as the surrounding ocean and sedimentary basins. Station data are most closely reproduced by a model in which the margin between the Glenburgh Terrane and the Yilgarn Craton (the Errabiddy Shear Zone) dips south, with crust of the Glenburgh Terrane wedged beneath the northern Yilgarn Craton. Forward modelling results also suggest that the main boundary between the Gascoyne Complex and the Pilbara Craton to the north is a steeply dipping structure beneath the Edmund and Collier Basins that may correlate with the Talga Fault.