Neoproterozoic Metamorphic Evolution of the Isbjørnhamna Group Rocks from South-Western Svalbard
A metamorphosed volcano-sedimentary complex constitutes the Caledonian basement in the south-western part of Wedel Jarlsberg Land, Svalbard. Field, textural and previous thermochronologic data indicate a weak, localized metamorphic Caledonian overprint (M2). Deformed M1 isograds and variation in pressure-temperature estimates indicate a pervasive Neoproterozoic amphibolite-facies metamorphism that pre-dates large-scale Caledonian age folding. Garnet-biotite and garnet-Al silicate-plagioclase (GASP) geothermobarometry of the Isbjornhamna Group mica schists, and their comparison with the K2O-FeO-MgO-Al2O3-SiO2-H2O (KFMASH) petrogenetic grid, indicates a peak pressure of ca. 11 kbar, and a peak temperature of ca. 670 degrees C during M1 metamorphism. A cooling rate of ca. 5 degrees C My(-1) is estimated on the basis of geothermobarometry and the available U-Th-total Pb and Ar-Ar data.