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Abstract
The metamorphic complexes of Tasmania formed during the Cambrian (ca 510 Ma) as a result of rapid compression in a subduction zone setting followed by rapid exhumation, which brought various fault-bounded metamorphic complexes back to the surface in less than 5 Ma. The two highest grade complexes, the Franklin Metamorphic Complex, and the Port Davey Metamorphic Complex, experienced initial growth of metamorphic garnets at ∼560°C, ∼0.56 GPa. However, their subsequent metamorphic histories diverge, with the FMC displaying a marked increase in pressure (to 1.4 GPa at peak P/T), while the PDMC shows only a slight increase in pressure (to ∼0.7 GPa). Both complexes show only a minor increase in temperature (∼100°C) between initial garnet growth and peak metamorphic conditions. Rapid exhumation of these complexes can be accounted for by a slab-breakoff model. However, the difference in peak pressure between these complexes requires either continued subduction of the FMC while the PDMC had already begun its return towards the surface or that the subduction zone geometry resulted in significantly different pressures occurring contemporaneously within portions of the channel, which are not far removed from one another.
ACKNOWLEDGEMENTS
Nick Turner and Dave Foster are thanked for taking the time to provide helpful reviews, which improved the quality of the manuscript. This research was made possible by a scholarship from the Tasmanian State Government through the auspices of Mineral Resources Tasmania with additional financial support from the University of Tasmania and CODES. Sample collection in the Collingwood River region of the Wild Rivers National Park was made possible by the Department of Primary Industries, Water and Environment and the National Parks and Wildlife (authority numbers ES 05278 and ES 06580).