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 natu ral cordierites across the Arendal amphibolite-granulite facies transi tion, 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 an d Li with metamorphic grade, while type-I H2O and Be are variable. The decrease of these volatiles and alkalies and the low total volatile c ontents of the granulite facies cordierites are best explained by prog ressive dehydration and decarbonation processes, possibly related to p artial melting. A progressive change of the X(H2O) = H2O/(H2O + CO2) r atio in the cordierites across the transition, as suggested by previou s studies, is not observed. Greenschist to low-amphibolite facies re-e quilibrated cordierites show a significant increase in either CO2, or H2O + CO2. Na is introduced at some localities. The retrograde fluid p hase is calculated to be CO2-rich.