Neoproterozoic metamorphic evolution of the Isbjørnhamna Group rocks from south-western Svalbard

Abstract

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 Isbjørnhamna 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°C during M1 metamorphism. A cooling rate of ca. 5°C My-1 is estimated on the basis of geothermobarometry and the available U–Th–total Pb and Ar–Ar data.