A Carbon Isotope Study of Graphites from the Kerala Khondalite Belt, Southern India: Evidence for $CO_{2}$ Infiltration in Granulites

Abstract

Field relations of arrested charnockite patches, felsic pegmatite dikes, and coarse cordierite + graphite veins in the granulite facies supracmstal belt of southern Kerala suggest paleo-fluid channels. We have investigated the stable isotopic composition of graphites associated with these structures, as well as those in association with charnockites adjacent to calcsilicate horizons. The remarkably high values displayed by graphites from the structurally controlled zones ( - 8.6 to - ), together with the narrow spread in individual localities (), correlate with precipitation from isotopically homogeneous -rich fluids that either infiltrated along structural pathways (faults/ shears) or were transferred through magmatic conduits. Graphites from charnockite-calcsilicate associations show extreme enrichment ( up to -4.8%). Changing fluid regimes are detected from up to variation in among graphites sampled adjacent to calcsilicate horizons and within single crystals of coarse graphite associated with cordierite-rich veins. Steep isotopic gradients across fluid channels, and the preservation of biogenic carbon signatures in disseminated graphite flakes within adjacent metapelites (), suggest that influx was strongly channelized. Our study provides evidence for graphite precipitation in reduced crustal lithologies infiltrated by -rich fluids and illustrates that graphite can be used as a potential monitor to detect infiltration in granulites.