Abstract

Polymetamorphosed gneisses of Proterozoic age crop out on Roan Mountain, North Carolina–Tennessee, near the western edge of the Blue Ridge belt. These gneisses display Grenville-age, granulite-facies assemblages, including two-pyroxene metabasites and gar-net-sillimanite-orthoclase metapelites. All gneisses were intruded by diabase dikes of the late Precambrian Bakersville Gabbro. Paleozoic amphibolite-facies metamorphism locally formed garnet and amphibole in mafic rocks and kyanite in metapelitic rocks.

Two pyroxene geothermometry and mineral stability curves define temperature-pressure ranges of 750–847 °C and 6.5–8.0 kbar for the granulite-facies metamorphism. This metamorphism probably occurred within the lower crust at depths of 23–28 km. Pressure-temperature conditions for the major Paleozoic metamorphism are not well constrained but are estimated to be 700–740 °C and 7.5–9.0 kbar.

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