Crustal magnetotelluric imaging of a Paleoproterozoic graphitic suture zone, Curnamona Province, Australia

Abstract

The Curnamona Province is a Paleoproterozoic to Mesoproterozoic domain that hosts the Broken Hill Pb-Zn ore body and a number of IOCG type Cu-Au deposits, but is mostly covered in Neoproterozoic to Quaternary cover. Three-dimensional resistivity modelling of 55-km gridded long-period (0.1–0.0001 Hz) magnetotelluric (MT) data collected as part of the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) previously revealed the presence of the Curnamona Conductor that exhibits extremely low resistivities <1 Ω.m at upper-crustal depths (<15 km) which has a lateral extent of >200 km in a north–south orientation. The conductor appears to dip to the west, centred under the large igneous province Benagerie Suite Volcanics with resistivity ∼10–100 Ω.m in a broader lower crustal region. To yield higher resolution of the Curnamona Conductor, a 56-site broadband (200–0.001 Hz) MT transect was undertaken with 2 km spacing. The east- west line intersected the observed conductive structures orthogonally. We show consistency between long-period MT AusLAMP 3D models, and new 2D and 3D broadband MT inversions, but with higher spatial and vertical resolution compared to the AusLAMP model.The linearity, depth extent and western dipping morphology of the Curnamona Conductor is remarkably similar to other Paleoproterozoic conductors in Australia along the eastern margin of the Mount Isa Province in northern Australia, and the eastern margin of the Gawler Craton in southern Australia. Plate reconstructions of Paleoproterozoic Nuna supercontinent suggests that these now disparate continental cratons were originally contiguous, with extensive subduction along their eastern margin between 2200 and 1850 Ma. Marine sedimentation in accretionary wedges prior to continental collision occurred during the Lomagundi-Jatuli Event, which recorded a global increase in δ13C (2300–2000 Ma) with a significant increase in burial of organic carbon. We argue that these Paleoproterozoic conductors thus represent graphitic suture zones that are uniquely representative of a time of enhanced carbon burial in Earth’s history.