Provenance of Palaeoproterozoic metasedimentary rocks in the eastern Gawler Craton, Southern Australia: Implications for reconstruction models of Proterozoic Australia.

Abstract

Detrital zircon ages obtained from the Corny Point Paragneiss and the Massena Bay Gneiss in the southeastern Gawler Craton, Australia, constrain their deposition to the interval ca. <1880 Ma. The presence of 2020 Ma, 2450 Ma and 2520 Ma detrital zircons within the Corny Point Paragneiss constrains the source region for the sedimentary protoliths to three possible domains within Australia; the Gawler Craton, the Glenburgh Orogen in the Western Australian Proterozoic, and the North Australian Craton, all of which contain rock systems with similar ages.

Whole rock εNd (1850Ma) values from the Corny Point Paragneiss range from -1 to -5. These values potentially preclude the Late Archaean to mid Proterozoic crust of the Gawler Craton as a sole or major source region due to its highly evolved average εNd (1850Ma) of around -10. Preclusion of the Gawler Craton as a source is apparently confirmed by Hf isotopic compositions of 2020 Ma detrital zircons from the Corny Point Paragneiss, which have εHf (2020Ma) ranging between +3 to +7. This compares with εHf (2020Ma) of -1 to -4 for zircons from the 2020 Ma Miltalie Gneiss in the Gawler Craton. Available Nd isotopic data suggests that the Glenburgh Orogen is too crustally evolved to have provided the majority of sediment into the Corny Point Paragneiss protolith. The 2020 Ma detrital Hf isotopic compositions of the Corny Point Paragneiss are similar to the 2020 Ma Wildman Siltstone (εHf (2020Ma) +2 to +7) in the Pine Creek Orogen in the North Australian Craton.

Two possible scenarios can be extrapolated from the detrital zircon and Nd isotopic data; (1) the Corny Point Paragneiss sediment was derived from a source region within the North Australian Craton and could share source regions with the Wildman Siltstone, or (2) the sediments were derived from a Gawler Craton source region that included a dominant juvenile component of the 2020 Ma Miltalie Gneiss in the adjacent Gawler Craton which has since been eroded. In the first scenario, the absence of connection to the Gawler Craton allows for the Betts and Giles (2006) plate reconstruction model, which proposes that the Corny Point Paragneiss formed part of the North Australia Craton, and was sutured to the Proto Gawler Craton at 1730-1700 Ma. The second scenario highlights a significant limitation in evaluating the significance of provenance data, particularly when considering old potential source terrains that have undergone significant levels of denudation. The proximity of the Corny Point Paragneiss to the rifted southern and eastern margins of the Australian Proterozoic means a thorough evaluation of the palaeogeographic significance of the Corny Point Paragneiss detrital signature requires corresponding datasets from regions such as Antarctica which were formerly contiguous with the Gawler Craton.