AN INFRARED SPECTROSCOPIC (IR) AND LIGHT-ELEMENT (LI, BE, NA) STUDY OF CORDIERITES FROM THE BAMBLE SECTOR, SOUTH NORWAY

Infrared absorption spectra and light element contents of several natural cordierites across the Arendal amphibolite-granulite facies transition, Bamble Sector, south Norway are presented. The infrared spectra record H2O (both type-I and type-II) and CO2 as fluid constituents in the channels, CO and hydrocarbons were not detected. Type-II water and (Ca + Na + K) are correlated and show a 2:1 molar ratio. The infrared and light element data indicate a decrease of Na, type-II H2O, CO2 and Li with metamorphic grade, while type-I H2O and Be are variable. The decrease of these volatiles and alkalies and the low total volatile contents of the granulite facies cordierites are best explained by progressive dehydration and decarbonation processes, possibly related to partial melting. A progressive change of the X(H2O) = H2O/(H2O + CO2) ratio in the cordierites across the transition, as suggested by previous studies, is not observed. Greenschist to low-amphibolite facies re-equilibrated cordierites show a significant increase in either CO2, or H2O + CO2. Na is introduced at some localities. The retrograde fluid phase is calculated to be CO2-rich.