Deep crustal magnetotelluric imaging of continental accretion and intracontinental deformation in central Australia

Abstract

Abstract Central Australia preserves a record of micro-continent and craton accretion during assembly of the Paleoproterozoic Nuna supercontinent 2500 − 1600 Ma, followed by Mesoproterozoic magmatic and orogenic events that formed the Musgrave Province. The Petermann Orogeny (630 − 520 Ma) and Alice Springs Orogeny (450 − 300 Ma) resulted in north-south crustal shortening and Moho offsets up to 20 km that yield gravity variations of ~ 160 mGals. Three-dimensional inversion of 614 long-period (10–10000 s) AusLAMP MT and 36 geomagnetic depth sounding (GDS) sites spaced ~ 55 km produced resistivity estimates to 250 km depth, covering 1500 km west-east, 1300 km north-south. From 0 to 5 km, resistivity maps the extent and thickness of Neoproterozoic Officer, Amadeus, Ngalia and Georgina Basins, and Mesozoic Eromanga basin. At all crustal depths the Arunta Province and northern Musgrave Province are resistive (> 10000 Ω.m), bounded by lower crustal conductive zones (< 10 Ω.m) to the north, east and south that align with suture zones associated with Paleoproterozoic accretion of ribbon continents. Lithospheric scale faults active in the Petermann Orogen (Woodroffe Thrust) and Alice Springs Orogen (Redbank Shear Zone) align with these low-resistivity zones, and we argue that graphite from carbon burial in Paleoproterozoic sediments reduces frictional strength and enable compressive deformation to localise strain.