Nd isotopic and geochemical constraints on provenance of sedimentary rocks in the Officer Basin, Australia: implications for the duration of the Petermann Orogeny.

Abstract

Nd isotopic data from Neoproterozoic to Ordovician sedimentary rocks in the eastern Officer Basin in southern Australia highlight the evolving provenance roles of the Gawler Craton and Musgrave Block basement complexes that bound the Officer Basin. Initial eNd values of around –16 for the early Neoproterozoic basal sequences (Pindyin Sandstone, Alinya Formation, and Tarlina Sandstone) indicate they were largely derived from the Archaean to Palaeoproterozoic Gawler Craton, which bounds the Officer Basin to the south. At around 640 Ma a major excursion of initial eNd values in the sedimentary sequence to around –9 indicates significant unroofing of the Mesoproterozoic Musgrave Block, which forms the northern margin of the basin. The uplift of the Musgrave Block at around 640 Ma is interpreted to mark the onset of the intracratonic Petermann Orogeny, which was a major orogenic event that shaped the lithospheric architecture of southern central Australia. Combined with existing isotopic and stratigraphic data, the isotope data from the eastern Officer Basin suggest that the Petermann Orogeny was a relatively long-lived event or series of events spanning a duration greater than 100 Ma. The change in initial eNd is accompanied by geochemical data that indicates slight elevation of mafic trace element indicators in the mid to late Neoproterozoic (Murnaroo Formation and Dey Dey Mudstone, Mena Mudstone Member), and earliest Cambrian (Arcoeillinna Sandstone). This is interpreted as contribution to the basin from the Musgrave Block, which is as a whole more mafic than the Gawler Craton. Subsequent to 640 Ma, eNd values of syn-Petermann Orogeny sediments diverge from the Musgrave Block trend, suggesting that there was an ongoing contribution from the Gawler Craton, despite the deposition of the sequences in the geographic foreland of the Petermann Orogen. The return toward a Gawler Craton provenance suggests that to a large extent, sediment derived from the Petermann Orogen bypassed the eastern Officer Basin for much of the Petermann Orogeny.