Orthopyroxene-bearing granitic (s. l.) gneiss and metamafic rocks and garne
t-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 investiga
ted is representative of the central part of the uplift, exposed in norther
n Boothia Peninsula and southern Somerset Island. Two types of fluid inclus
ions predominate in quartz of the gneisses: CO2 with admired methane or nit
rogen, and brine. Temperatures and pressures calculated from garnet - ortho
pyroxene -plagioclase - quartz and garnet - sillimanite - plagioclase - qua
rtz equilibria mostly fall in the ranges 740 degrees-850 degrees C and 6-8
kbar. One sample of garnet-orthopyroxene tonalite gneiss has preserved a re
cord of what may be peak or near-peak conditions of metamorphism: 960 degre
es C and 8.7 kbar. Cordierite-bearing paragneisses yield less than or equal
to 650 degrees C and <5 kbar, reflecting the retrograde formation of cordi
erite during decompression and cooling. The Boothia-Somerset granulite terr
ane probably represents an extension of the 1.9-2.0 Ga Taltson-Thelon oroge
n, noted far 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.