The structure and metamorphism of the Red Point Metamorphic Complex—A newly discovered high-pressure metamorphic complex from the south coast of Tasmania

Abstract

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.

KEY WORDS:

• Tyennan Orogeny
• Tasmania
• high P metamorphism
• structure
• Ross Orogeny
• Delamerian Orogeny

ACKNOWLEDGEMENTS

We thank the Tasmanian Department of Primary Industries, Water and Environment and the National Parks and Wildlife Service for permission to undertake fieldwork and sampling in the Southwest National Park. This project was funded through the ARC Centre of Excellence in Ore Deposits. A. McNeill is thanked for his involvement in organising the early stages of this project, K. Goemann, S. Feig, and S. Meffre are thanked for analytical assistance, and L. James is thanked for assistance in the field. David Gray and Solomon Buckman are thanked for their detailed reviews and insightful comments on collision zone tectonics.