Charnockites, pyroxene granulites, and garnet-cordierite gneisses at a boundary between Early Svecofennian rocks and Småland-Värmland granitoids, Karlskoga, southern Sweden

Abstract

Abstract A lobe of Early Svecofennian high-grade, metamorphic rocks surrounded and intruded by rocks of the Smaland-Varmland batholith east of Karlskoga, central southern Sweden, has been studied. Application of geothermobarometry reveals that these rocks have suffered granulite facies metamorphism at conditions constrained to 670–770°C, 4.0–4.5 kbar and aH2O0.1–0.3. The metamorphism has transformed biotite granite into charnockite, intermediate volcanite into pyroxene granulite, and lower grade presumably semipelitic gneiss into garnet-cordierite gneiss. Extensive partial melting accompanied the metamorphism in the garnet-cordierite gneisses and granulites, but not in the charnockites. The metamorphism is attributed to a local contact metamorphic peak, associated with the emplacement of the Smaland-Varmland granitoids and related mafic plutonics, in the penecontemporaneous, amphibolite facies, regional “serorogenic Svecofennian” episode.