REACTION HISTORY OF SAPPHIRINE GRANULITES AND A DECOMPRESSIONAL P-T PATH IN A GRANULITE COMPLEX FROM THE EASTERN GHATS

The sapphirine granulites from G. Madugula, Eastern Ghats preserve a v ariety of mineral textures and reactions. Corona and reaction textures are used in conjunction with mineral compositions to construct a sequ ence of metamorphic reactions describing the mineralogical evolution o f sapphirine granulites. An early stage is characterized by the develo pment of sapphirine + quartz, spinel + quartz in textural equilibrium, and possible relicts after osumilite during peak metamorphic conditio ns. Sapphirine/spinel crystals were later detached from quartz in the form of mineral coronas. During a subsequent sapphirine-cordierite sta ge, several cordierite forming reactions reflect decreasing P-T condit ions. Finally during the late stage, a few samples show evidence of re trogressive hydration. Sapphirine is rather icon-rich (12.8wt%) and th e Mg number in the analysed minerals varies in the order: cordierite > phlogopite > sapphirine > orthopyroxene > spinel > garnet. P-T condit ions of metamorphism have been constrained through the application of geothermobarometry and thermodynamically calibrated MAS equilibria. P- T vectors from granulite facies rocks in the G. Madugula area indicate that the rocks experienced substantial decompression (up to 3kbar) an d moderate cooling (150-200 degrees C) subsequent to peak conditions o f metamorphism (8.4kbar, > 900 degrees C). The decompressional P-T his tory of sapphirine granulites interpreted from textural features and t hermobarometric estimates suggest that they may have eventually result ed from exhumation of thickened crust.