Chemical U - Th - Pb monazite dating and the Proterozoic history of King Island, southeast Australia

Abstract

The Proterozoic stratigraphy of Tasmania has some common aspects with South Australia but the Wickham Orogeny (760 Ma) has been a major contrasting feature. We have used chemical U-Th-Pb monazite dating to clarify the age relationships in western King Island, which is the key area for the definition of the Wickham Orogeny. New monazite dates demonstrate that the major regional deformation on King Island occurred at 1290 Ma. The Wickham Orogeny is reinterpreted as a local deformation restricted to the contact aureole of the Cape Wickham granite. The Wickham Orogeny in Tasmania may correlate with minor felsic volcanism in the Adelaide Fold Belt, and low-angle unconformities in the Neoproterozoic of northwest Tasmania. The metamorphism on King Island is synchronous with Grenville-age (1300 Ma) orogenic events recognised in central and western Australia. The nearest known examples to Tasmania are in the Musgrave Ranges. Monazite dating of western King Island provides the first direct evidence for Mesoproterozoic basement in southeastern Australia and has major implications for Rodinia reconstructions.