A revised Proterozoic tectono-stratigraphy of the South Nicholson region, Northern Territory, Australia—insights from SHRIMP U–Pb detrital zircon geochronology

Abstract

New SHRIMP U–Pb detrital zircon geochronology on Mesoproterozoic and Paleoproterozoic siliciclastic rocks from the South Nicholson region, in concert with recently acquired complementary regional geophysical datasets, have enabled comprehensive revision of the regional Proterozoic tectono-stratigraphy. The identification of analogous detrital zircon spectra of units deposited in half-graben hanging walls of major east-northeast-trending extensional faults, offers compelling evidence for regional tectono-stratigraphic correlation. This study sampled units from the hanging walls of the Benmara, Bauhinia, and Maloney-Mitchiebo (east-northeast-trending) faults, which identified immature proximal lithofacies hosting a small yet persistent population of ca 1660–1640 Ma aged zircon and lack Mesoproterozoic detritus. The timing of this event is consistent with deposition coincident with crustal extension during the extensional River Event at ca 1640 Ma, an event previously identified from the Lawn Hill Platform in western Queensland. This finding suggests the hanging wall sequences are chrono-stratigraphically equivalent to the highly prospective sedimentary rocks of the Isa Superbasin, host to world-class sediment-hosted base metals deposits across western Queensland and northeastern Northern Territory. Subsequent inversion of the extensional faults resulted in development of south-verging thrusts, and exhumation of late Paleoproterozoic hanging wall siliciclastic rocks through overlying Mesoproterozoic South Nicholson Group rocks as fault propagated roll-over anticlines. These geochronology data and interpretations necessitate revision of the existing stratigraphy and the renaming of a number of stratigraphic units in the South Nicholson region. Accordingly, the distribution of the highly prospective late Paleoproterozoic units of the McArthur Basin, Lawn Hill Platform and Mount Isa Province is greatly expanded across the South Nicholson region. These findings imply that the underexplored South Nicholson region is a highly prospective greenfield area for energy and mineral resources. KEY POINTS SHRIMP U–Pb detrital zircon geochronology provides a basis for revision of the Proterozoic stratigraphy in the South Nicholson region. Correlation of sedimentary units across the region is based on closely matching zircon age spectra, lithofacies and tectono-sedimentary setting. Revision of the Proterozoic stratigraphy increases the prospectivity for sediment-hosted base metal resources across the South Nicholson region.