Thermobarometry of the charleston metamorphic group and implications for the evolution of the paparoa metamorphic core complex, New Zealand

Abstract

The Charleston Metamorphic Group in the central Paparoa Range, southwest Nelson, New Zealand, comprises metasedimentary and granitoid lithologies that have been metamorphosed to sillimanite‐almandine conditions. Mineral assemblages and thermobarometric calculations indicate metamorphic temperatures and pressures of c. 600 (±50)°C and 4 (±1) kbar, respectively. A K‐feldspar‐sillimanite isograd mapped in pelitic gneisses indicates that metamorphic grade increases to the southwest, though this is not verified by thermobarometry results, which vary little throughout the entire range. A strong foliation is present in all lithologies. This foliation is folded but typically strikes between north and northeast. The gneisses are intruded by several postmetamorphic granitoids, which in places retain their primary magmatic foliation (commonly striking between north and west), are unfolded and unmetamorphosed. These granitoids are distinct from the orthogneisses within Charleston Metamorphic Group. Together, the granitoids and gneisses comprise the Paparoa Metamorphic Core Complex, which was uplifted and unroofed in the mid Cretaceous, when estimated geothermal gradients were 50–90°C/km and uplift rates were 0.6–1.0 mm/a. © 1994 The Royal Society of New Zealand.