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Abstract
Chemical U – Th – Pb dating of monazite from 12 schists throughout western and central Tasmania define a peak metamorphic age of ca 510 Ma. This age is very close to the age of arc – continent collision and ophiolite emplacement, implying very rapid uplift and cooling. To the south, along the western margin of the South Tasman Rise, metamorphism occurred later at 495 Ma, which correlates with a late stage of the Ross Orogeny, Antarctica. The Tyennan Orogeny in Tasmania has a three-stage history similar in age to the Delamerian Orogeny in South Australia. However, the Tyennan Orogeny only produced metamorphic rocks during the early stage associated with ophiolite obduction at 515 – 505 Ma. The intense compressional event recognised in the Delamerian and Ross Orogeny at 500 – 495 Ma is correlated with a mild basin inversion in Tasmania, and no metamorphism on mainland Tasmania has been recognised associated with this event. The western margin of the South Tasman Rise is a fragment of the Ross Orogen and does not correlate directly with Tasmania.
Acknowledgements
Many of the samples for this study come from the collection at the University of Tasmania. They were collected by many staff and students of the university over the last 50 years, in particular Rob Lewis, Andrew McNeill, Marcel Kamperman and Alan Spry. The study was supported by an IRGS grant from the University of Tasmania. David Seymour and Chris Fergusson are thanked for their constructive reviews that have added significantly to the clarity of this paper.
Notes
*Tables 3 and 4 [indicated by an asterisk (*) in the text and listed at the end of the paper] are Supplementary Papers; copies may be obtained from the Geological Society of Australia's website (www.gsa.org.au) or from the National Library of Australia's Pandora archive (http://nla.gov.au/nla.arc-25194)