Lithospheric architecture of the Curnamona Province, Australia

Abstract

The Curnamona Province in southern Australia is a 90,000 km² Paleoproterozoic to Mesoproterozoic craton that rifted from the Gawler Craton in the Neoproterozoic and is now separated by the Adelaide Rift Complex sediments in the Flinders Ranges. Magnetotelluric (MT) surveys have been conducted across the Curnamona Province to provide insights on lithospheric architecture. A long-period (10–10,000 s) MT inversion of 136 AusLAMP and legacy long-period MT sites, 134 broadband MT, and 31 geomagnetic depth sounding (GDS) sites over an area 500 km by 500 km is used to create a lithospheric-scale framework for the province. In addition, a crustal-scale broadband (0.01 to 1000 s) MT inversion of 134 sites with closer spacing yields higher fidelity of crustal heterogeneity. The long-period Curnamona Province model is combined with other regional models across southern Australia, encompassing the Archean-Mesoproterozoic Gawler Craton in the west to the Phanerozoic Delamerian and Lachlan Orogens in the east. In this wider context, the Curnamona Province is shown to exhibit four distinct regions of low resistivity. (a) In the top 5 km, resistivity is most strongly influenced by the porosity of sedimentary cover. (b) The upper crust to a depth of 20 km has low resistivity < 1 Ω.m along the eastern margin of the province possibly from organic carbon deposited in the Paleoproterozoic. (c) The lower crust to the Moho (∼40 km) has low resistivity (<100 Ω.m) and is coincident with the extent of the Adelaide Rift Complex suggesting it may have resulted during a period of Neoproterozoic rifting. (d) At sub-continental lithospheric depths of 150–250 km, high electrical conductance in the central to northern part of the Curnamona Province is attributed to metasomatism at the base of the lithosphere in the Mesoproterozoic.