Fluid Inclusions in Granulites and Eclogites from the Bergen Arcs, Caledonides of W. Norway

T. Andersen, H. Austrheim and E. A. J. Burke
Mineralogisk-Geologisk Museum, University of Oslo, N-0562 Oslo 5, Norway
Instituut vor Aardwetenschappen, Vrije Universiteit, Amsterdam, The Netherlands

Abstract: The Grenvillian granulite-facies complex on Holsnøy island, Bergen Arcs, W. Norway, has been metamorphosed at eclogite-facies conditions during the Caledonian orogeny (ca. 425 Ma). The granulite-eclogite facies transition takes place along shear zones and fluid pathways. Mineral thermobarometry indicates PT conditions of 800–900°C and 8–10 kbar for the Proterozoic granulite facies metamorphism and 700–800°C and 16–19 kbar for the eclogite-forming event. Quartz in the granulite facies complex contains CO2 fluid inclusions with less than 2.5 mole percent N2; the molar volumes are compatible with the PT conditions of the Proterozoic granulite metamorphism. Quartz in pegmatitic quartz + omphacite and quartz + phengite/paragonite veins coeval with shear-zone eclogites contain N2 ± CO2 fluid inclusions. Combined laser Raman microanalysis and microthermometry show that the least disturbed inclusions have XCO2 = 0.1–0.3, and molar volumes less than 40 cm3/mole, which may agree with the PT conditions during Caledonian high-pressure metamorphism. Younger, low-density N2 and N2-H2O fluid inclusions are the results of decrepitation and redistribution of early inclusions during the retrograde PT evolution of the eclogites.

Keywords: granulite • eclogite • fluid inclusions • carbon dioxide • nitrogen • Bergen Arcs • Norway

Mineralogical Magazine; June 1990 v. 54; no. 375; p. 145-158; DOI: 10.1180/minmag.1990.054.375.02
© 1990, The Mineralogical Society
Mineralogical Society (www.minersoc.org)