Metamorphic Conditions at an Amphibolite-Granulite Transition Zone in RogalanWest Agder, SW Norway
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Geological Sciences Senior Theses; 1996
The geology of Southwest Norway is dominated by amphibolite-granulite facies gneisses along with granitic migmatites and other intrusive bodies. Previous work (see references) indicates that four distinct metamorphic events took place in this region. The complex metamorphic history began with two high-grade events at 1.45 Ga (M 1) and 1.0 Ga (M2). These two events were followed by regional cooling and formation of retrograde metamorphism (M3). This retrograde metamorphism and partial reequilibration of certain mineral phases have created a challenge when trying to estimate pressures and temperatures in the area. Pressure and temperature for the M2 event has been estimated to 750°C and 3.5-4.0 kb (Bakker, 1993) and to 750°C and 3.5-4.0 kb (Miller et. al. 1992) for the rocks near the transition zone. Five thin sections representing the transition zone were selected for this study. A Cameca SX-50 Electron Microprobe was used to analyze the samples for chemical composition. Results from calculations using the Holland-Blundy amphibole-plagioclase thermometers indicate temperatures ranging between 750 OC and 840 OC at pressures 3.5- 5.0 kb.