Provenance history of the Bangemall Supergroup and implications for the Mesoproterozoic paleogeography of the West Australian Craton.

Abstract

The 4-10 km-thick Bangemall Supergroup, comprising the Edmund and Collier Groups, was deposited between 1620 and 1070 Ma in response to intracratonic extensional reactivation of the Paleoproterozoic compressional Capricorn Orogen. The supergroup can be further divided into six depositional packages bounded by unconformities or major marine flooding surfaces. U-Pb dating of over 1200 detrital zircon grains from 19 samples representative of each of the major sandstone units within these packages has failed to identify any zircon populations attributable to syndepositional magmatism. However, this extensive dataset provides a provenance history of the Bangemall Supergroup, which is here integrated with paleocurrent data which indicates that all source areas were located within the Mesoproterozoic West Australian Craton, with the main source area for the northern Bangemall Supergroup being the Gascoyne Complex and southern Pilbara Craton. All samples have prominent age modes in the 1850-1600 Ma range, indicating significant contribution from the northern Gascoyne Complex and coeval sedimentary basins. Some samples also display prominent modes in the 2780-2450 Ma range, consistent with derivation from the Fortescue and Hamersley Groups of the southern Pilbara Craton.The Edmund Group has age-spectra in which the dominant modes become older upwards, recording unroofing of the underlying basement from the Gascoyne Complex to the Archean granites and greenstones of the Pilbara Craton. In contrast, the Collier Group records unroofing of the underlying Edmund Group, with possible additional contribution from the Pilbara Craton and Paterson Orogen, and is characterized by age-spectra in which the dominant modes become younger upwards. These data imply that the West Australian Craton remained intact throughout the Mesoproterozoic assembly of Rodinia, and was the only source of detritus for the Bangemall Supergroup.