Preservation of premetamorphic oxygen and carbon isotopic trends in granulite facies marbles from Rogaland, southwest Norway

Abstract

Calcites in marbles from the very high-grade Precambrian terrain of Rogaland, southwest Norway, show a regional trend from δ18OCal = 21.5‰ (SMOW) and δ13CCal = -3.2‰ (PDB) near the contact with the magmatic complex, to δ18OCal = 13.1‰ and δ13CCal = -8.2‰ about 30 km farther north. This trend has an opposite direction to the typical δ18O and δ13C depletion trends observed in carbonate rocks from other metamorphic aureoles. It is concluded that the dry granulite facies metamorphism resulting from intrusion of the magmatic complex merely preserved premetamorphic bulk isotopic characteristics of the marbles. Isotopic inhomogeneity among distinct metamorphic minerals like calcite, quartz, and diopside in marbles, quartz-diopside gneisses, quartzites, and enderbitic gneisses, both on outcrop and on regional scale, precludes pervasive regional passage of significant quantities of isotopically homogeneous oxygen-bearing metamorphic fluids. -from Authors