Tasmania in Nuna: Witness to a ~1.4 Ga East Antarctica–Laurentia Connection

Abstract:

Most recent reconstructions of the supercontinent Nuna juxtapose the North Australian craton, Mawson continent (South Australia–East Antarctica), and Laurentia between 1.6 Ga and 1.3 Ga, but differ in their relative positioning. Tasmania (SE Australia) has not been considered in previous Nuna reconstructions. Prior to late Neoproterozoic rifting, this crustal fragment was likely part of the eastern margin of East Antarctica. The significance of Tasmania’s position within Nuna has recently been highlighted with the discovery that the majority of a >10-km-thick marine shelfal package exposed in northwest Tasmania (Rocky Cape Group) was deposited between 1.45 and 1.30 Ga. The detrital zircon signatures of these strata are distinct from other Mesoproterozoic basins in Australia, and instead closely resemble time-equivalent upper parts of the Belt-Purcell Basin of Laurentia, suggesting correlations within Nuna.

We investigate the provenance of the Rocky Cape Group quartzites by comparing new detrital zircon U-Pb-Hf isotopic data to an extensive compilation of zircon data from Australia, East Antarctica, and Laurentia. Our analysis demonstrates that the Rocky Cape Group is unlikely to have been sourced from any geological terrane exposed in present-day Australia. Instead, zircon isotopic signatures from basement terranes in Laurentia and East Antarctica show striking similarities to the Rocky Cape Group detrital signature. Paleocurrent data indicate a northwest-southeast–trending paleoshoreline
and suggest that the majority of sediment was sourced from Paleoproterozoic crust in SW Laurentia, which was to the southeast (present-day coordinates) of Tasmania. These new data support a SWEAT-like (southwest United States–East Antarctica) configuration for Nuna. We suggest that rifting propagated southward from ca. 1.4 Ga, leaving a thinned continental connection between East Antarctica and southwest Laurentia onto which the lower-middle RCG was deposited prior to 1.3 Ga.