A new occurrence of sapphirine-bearing granulite from Podur, Andhra Pradesh, India

Summary

We report here on a new occurrence of sapphirine bearing granulites in the high-grade granite gneisses from Podur. Podur is situated in the north-eastern part of the Eastern Dharwar Craton about 150 km NNE of Hyderabad, India. The common stable assemblage contains cordierite-biotite-sapphirine-spinel-corundum-K-feldspar. Interpretation of multiphase reaction textures in conjunction with mineral chemical data and topology in the (Fe,Mg)O-(Al₂O₃-K₂O)-(SiO₂-6K₂O) system is consistent with the following reactions: ${\rm biotite} + {\rm corundum} = {\rm spinel} + {\rm K\hbox{-}feldspar} + {\rm H_2O}$ ${\rm phlogopite\ (in\ biotite)} + {\rm corundum} = {\rm eastonite\ (in\ biotite)} + {\rm spinel} + {\rm cordierite}$ ${\rm spinel} + {\rm cordierite} = {{\rm sapphirine}_{2:2:1}}^{*}$ ${\rm cordierite} + {\rm biotite} + {\rm corundum} = {{\rm sapphirine}_{7:9:3}}^{*} + {\rm K\hbox{-}feldspar} + {\rm H_2O}$ ${\rm sapphirine}_{7:9:3} + {\rm biotite} = {\rm cordierite} + {\rm spinel} + {\rm K\hbox{-}feldspar} + {\rm H_2O}$ ${\rm sapphirine} = {\rm cordierite} + {\rm spinel} + {\rm corundum}$

The P–T evolution of these sapphirine granulites has been constrained through the use of conventional geothermobarometry and THERMOCALC program. The P–T conditions of metamorphism from different pertinent calibrations are estimated to be around 6.5–7.0 kbar and 750–800 °C, respectively. On the basis of the available evidence for a 2.6 Ga granulite facies event in the Karimanagar granulite belt, the emerging concept of East Gondwana assembly is endorsed.