Pressure-Temperature Conditions of Granulite Formation in Rogaland, SW Norway

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The Ohio State University

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The geology of SW Norway is dominated by high-grade amphibolite to granulite facies gneisses with associated migmatites and anorthosite-magerite complexes. Previous work suggests that metamorphism consisted of two high temperature events at 1.45 Ga (MI) and 1.0 Ga (M2), followed by regional cooling and formation of retrograde assemblages (M3). Partial reequilibration of certain mineral phases has led to some uncertainty about the pressures of metamorphism and whether the retrograde assemblages represent a discrete metamorphic event. Pressure and temperature conditions of the M2 metamorphism of gneisses located near the osumilite-in isograd were constrained using gt-opx, opx-bt, cord-btgt, and gt-sill-qt-plag equilibria. Core compositions were used for all ferromagnesium phases to avoid the effects of Fe-Mg exchange during cooling. Results suggest that peak metamorphism occurred at pressures of 5-6 kb and temperatures of 71O-800°C. Rim temperatures and pressures were estimated at 490-550°C and 4-5 kb, suggesting retrograde metamorphism, and possibly implying isobaric cooling.



Norway, metamorphism