Colour-Coded Compositional Mapping of Reaction Textures in a Calc-Silicate-Charnockite Interface at Nuliyam, Kerala

Colour-coded compositional mapping under an electron microprobe provides useful information on chemical gradients within the domain of individual minerals. Here we apply this technique to granulite facies reaction textures from a calc-silicate-charnockite interface at Nuliyam, southern Kerala, to understand the element mobility patterns and mass balance related to fluid-induced metasomatism during deep crustal metamorphism. The contact zone assemblage at Nuliyam is characterized by plagioclase + quartz symplectites after K-feldspar. From element mapping of this reaction interface on micron - scale, and from quantitative analyses of the individal mineral phases under an electron microprobe, we trace the diffusion of K, and addition of Na and Ca, through an open system migration dUling the influx of externally-derived CO₂-rich fluids. Our study provides the first direct evidence for microscale chemical diffusion associated with CO₂-induced charnockite formation in southern Kerala, and illustrates the potential of colour-coded compositional mapping in tracing element mobility patterns.