The Flinders Conductivity Anomal(ies) Revisited Using AusLAMP Magnetotelluric Data

Abstract

We use 74 stations from the long period eventual-Australia-wide AusLAMP (Australian Lithospheric Architecture Magnetotelluric Project) dataset to image the electrical resistivity beneath the Neoproterozoic Ikara-Flinders Ranges and adjacent Paleo-Mesoproterozoic Curnamona Province. Results from 3D inversions using ModEM software show a relatively resistive Ikara-Flinders Ranges, with two parallel arcuate conductors at 20 to 80 km depth in the Nackara Arc. There is a good correlation of diamondiferous kimberlites occurring over conductors, which we interpret as evidence for these conductors to be residing on large lithospheric structures that have been conduits for partial melt and volatile movement in the Jurassic period. The Curnamona Province is remarkably conductive for a region that is thought to have a cratonic core, with Delamerian reworking only at its edges. We see an enriched crust that covers most of the province at depths of 10–40 km. The presence of the conductor at lower crustal depths suggests that conductive sediments cannot entirely explain the conductor. We suggest that fluids associated with subduction have pervasively modified the crust in the past, resulting in an enrichment of carbon and sulphides, enhancing conductivity. Additionally, we conclude that the notion of a single continuous arcuate Flinders Conductivity Anomaly is unlikely and that the anomalous response observed is instead a result of the combined response of three separate anomalies; the Curnamona Province Conductor and the two Nackara Arc Conductors.