The role of fluids in the development of a granulite facies transition zone in S India

The Bodinayakkanur area of Tamil Nadu lies in the transition zone (P = 5 kbar, T = 700°C) from amphibolite to granulite facies metamorphism, in the Archaean high grade terrain of S India. Within the zone 3 closely associated rock units occur: (1) Precursor grey gneiss. (2) Pink migmatitic and metasomatic gneiss, (3) Green charnockitic granulites. Field observation shows that the complex inter-relations between these 3 rock types can be related to influx of fabric- and layer-guided CO 2 - and H 2 O + K 2 O-rich fluid phases, derived from a deep-seated source.