Gneisses from the granulite terrane of the Central Boothia Uplift, Arctic Canada

Orthopyroxene-bearing granitic (s.l.) gneiss and metamafic rocks and garnet-sillimanite paragneiss, which underwent granulite-facies metamorphism and intrusion by syenitic magma 1.9 Ga ago, constitute the bulk of the highly deformed crystalline core of the Boothia Uplift. The sample suite investigated is representative of the central part of the uplift, exposed in northern Boothia Peninsula and southern Somerset Island. Two types of fluid inclusions predominate in quartz of the gneisses: CO₂ with admixed methane or nitrogen, and brine. Temperatures and pressures calculated from garnet - orthopyroxene - plagioclase - quartz and garnet - sillimanite - plagioclase - quartz equilibria mostly fall in the ranges 740°-850°C and 6-8 kbar. One sample of garnet-orthopyroxene tonalite gneiss has preserved a record of what may be peak or near-peak conditions of metamorphism: 960°C and 8.7 kbar. Cordierite-bearing paragneisses yield ≤650°C and <5 kbar, reflecting the retrograde formation of cordierite during decompression and cooling. The Boothia-Somerset granulite terrane probably represents an extension of the 1.9-2.0 Ga Taltson-Thelon orogen, noted for its high-temperature metamorphism and magmatism, but is marked by a distinctive syntectonic intrusive suite and the presence of gneissic protoliths of earliest Proterozoic age.