EXTREMELY HIGH-TEMPERATURE CALCAREOUS GRANULITES FROM THE EASTERN GHATS, INDIA - EVIDENCE FOR ISOBARIC COOLING, FLUID BUFFERING, AND TERMINAL CHANNELIZED FLUID-FLOW

A suite of calc-silicate and calc-magnesian silicate granulites from B orra, Eastern Ghats belt, India, displays six critical mineral assembl ages that were produced from widely varying bulk compositions at diffe rent episodes of metamorphism. Phase equilibria considerations in the calcareous rocks and geothermobarometry in associated rocks attest to metamorphic temperatures in excess of 950-degrees-C at moderate pressu res (9 kbar). Subsequently, the complex evolved through a near-isobari c cooling path (DELTAP = 2 kbar, DELTAT = 250-degrees-C) that intersec ted several vapour-absent equilibria. Fluid composition was regionally buffered by mineral equilibria both during peak and retrograde metamo rphism, and as a result of varied bulk compositions X(CO2)fl varied be tween approximately 0.8 and approximately 0.4 in microscale during pea k metamorphism. However, increased CO2 activity (promoted by channeliz ed CO2 flux) along late narrow shear zones is locally indicated by min eral equilibria. Carbon and oxygen isotopic data reveal that the calca reous rocks preserved gradients presumably from the premetamorphic sta ge, which rule out any pervasive fluid flux during granulite facies me tamorphism in Eastern Ghats.