Abstract
Abstract Carbon dioxide-rich inclusions commonly occur in banded charnockites and khondalites of southern Kerala as well as in incipient charnockites formed along oriented zones by desiccation of gneisses. Combined pressure-temperature data from solid phases and CO2 equation of state barometry from fluid inclusion isochores depict that high density carbon dioxide was the dominant ambient fluid species in all the three rocks. Carbon stable isotope analysis of the fluids using a stepped heating technique in samples collected from Ponmudi, Kottavattom, Manali and Kadakamon show that the banded charnockites and gneisses contain ca. 50-60ppm carbon with d13C values in the range of -8 to -12.3‰. The incipient charnockites are characterised by abundant CO2 (upto 200 ppm) with d13C in the range, -7.5 to -10.3‰. The carbon stable isotope value of + 1.2‰ obtained for calc-silicate is in ccntrast to the value for the intercalated banded charnockite from Kadakamon (-10‰) depicting that decarbonation was not the source of CO2, Whereas the heavier carbon-enriched nature of incipient charnockite from Manali may suggest a juvenile source, the carbon isotope values in Ponmudi and Kottavattom suggest a mixed source, possibly due to the interaction of externally derived CO2 with graphite in the rocks.
Published Version
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