Abstract
Geothermometry and geobarometry of orthogneisses and metasediments across the Pikwitonei granulite facies domain of central Manitoba shows an increase of paleopressure from about 6 kbar near the orthopyroxene isograd on the east to 12 kbar near the western boundary against the Thompson Nickel Belt. The most consistent geobarometers are based on the assemblage garnet-orthopyroxene-plagioclase-quartz. Associated temperatures determined from various geothermometers are mainly in the range of 700-800°C, indicating, with the paleopressures, a steep dP/dT gradient during late Archean metamorphism. Metasedimentary assemblages within the Thompson Belt indicate amphibolite facies metamorphic conditions near 650°C and 4.5 kbar, which probably resulted from a mid-Proterozoic (Hudsonian) closure of a continental rift. A few outliers of granulite facies within the Thompson Belt record metamorphic conditions similar to those of the Pikwitonei domain and are probably relics which survived the later event. It is postulat...
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