Coupled laser Raman spectroscopy and carbon stable isotopes of graphite from the khondalite belt of Kerala, southern India

Abstract

Graphite in high grade meta-supracrustal rocks provide an important proxy to characterize biogenic and abiogenic carbon sources. Here we investigate graphite in various associations within the granulite facies metapelites (khondalites) of Kerala in southern India with a view to characterize the textural varieties and their genesis through the application of laser Raman spectroscopy and carbon isotopes. We trace the increasing intensity of metamorphism from the Raman spectra of the different graphite types. The δ13C values of the graphite show two distinct origins; the relatively lighter values in the range of −17.5‰ to −20.7‰ represent a mixture of biogenic and magmatic carbon, whereas the heavier isotopes in the range of −11.7‰ to −13.8‰ are suggested to present graphite precipitation from CO2-rich fluids from sub-crustal magmatic sources. Our study provides insights on the spectral properties of graphite in relation to the intensity of metamorphism and also reveals both biogenic and abiogenic sources of carbon.