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The Proterozoic Oonah Formation comprises a thick sequence of turbidites and mafic rocks that is widely exposed in western and northern Tasmania. The regional significance of the Oonah Formation is poorly understood as its contacts are faulted and estimates of its depositional age range from 1450 Ma to 700 Ma. Here we refine the depositional age of the Oonah Formation and clarify its relationship to other Proterozoic sequences in Tasmania. Magmatic apatite from the syn-sedimentary Cooee Dolerite has a 207Pb-corrected 238U/206Pb age of 733 ± 9 Ma that provides a robust estimate of the depositional age of the Oonah Formation. The Oonah Formation contains abundant 750 Ma detrital monazite and has detrital zircon age populations at 1800-1700 Ma, 1590 Ma, and 1450 Ma. The new age and provenance data support the interpretation that the Oonah Formation is a lateral equivalent of the base of the Togari Group and correlatives in Tasmania. We demonstrate that the stratigraphy and provenance of Neoproterozoic strata in Tasmania differ from time-equivalent sequences in Adelaide Rift Complex but are similar to the Pahrump Group (Death Valley, California) and the Cobham Formation (Transantarctic Mountains), which supports a southwest Laurentia—Tasmania—East Antarctica connection within supercontinent Rodinia. [ABSTRACT FROM AUTHOR]

This study presents new data on the deformational and metamorphic history of previously unstudied Cambrian high-pressure metamorphic rocks exposed on the remote south coast of Tasmania. The Red Point Metamorphic Complex consists of two blocks of high-pressure, medium-grade metamorphic rocks including pelitic schist and minor garnet-bearing amphibolite, which are faulted against a sequence of low-grade phyllite and quartzite. The Red Point Metamorphic Complex records five phases of deformation, all of which except the first are expressed at a mesoscopic scale in both the medium- and low-grade rocks. Peak metamorphic conditions in the high-pressure epidote–amphibolite facies is recorded by medium-grade schist and amphibolite and was synchronous with the second major deformation event, which produced a pervasive schistosity and mesoscale isoclinal folds. The juxtaposition of the low- and medium-grade rocks is interpreted to have first occurred prior to the development of upright, opening folding associated with the third deformation. However, the present contacts between the two contrasting metamorphic sequences formed during widespread faulting and ductile-shear zone development associated with the fourth and fifth deformation events. The new data from the Red Point Metamorphic Complex provide insights into the structural and metamorphic history experienced by the medium-grade rocks of Tasmania during the Cambrian Tyennan Orogeny. This study demonstrates that Cambrian medium-grade metamorphic rocks are more widespread throughout Tasmania than previously realised, which represents an important step towards understanding the large-scale architecture of the Tyennan Orogen. [ABSTRACT FROM AUTHOR]