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

Calcites in marbles from the very high-grade Precambrian terrain of Rogaland, southwest Norway, show a regional trend from delta(18)O(Cal) = 21.5 permil (SMOW) and delta(13)C(Cal) = -3.2 permil (PDB) near the contact with the magmatic complex, to delta(18)O(Cal) = 13.1 permil and delta(13)C(Cal) = -8.2 permil about 30 km farther north. This trend has an opposite direction to the typical delta(18)O and delta(13)C depletion trends observed in carbonate rocks from other metamorphic aureoles. In the marbles, the oxygen isotopic trend in calcites is concordant with oxygen isotope ratios of the high-grade metamorphic silicates diopside and phlogopite. No regional delta(18)O trends have been observed either for quartz or diopside in quartz-diopside gneisses and quartzites of the or same metasedimentary succession nor in quartz, plagioclase, and orthopyroxene in enderbitic gneisses enveloping the metasediments. 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 of significant quantities of isotopically homogeneous oxygen-bearing metamorphic fluids. This is in accordance with petrologic observations throughout the area.