A corundum-quartz assemblage from the Eastern Ghats Granulite Belt, India: Evidence for high P-T metamorphism?

Corundum+quartz-bearing assemblages occur in small lenses in granulite facies metapelites in Rayagada, north-central part of the Eastern Ghats Granulite Belt, India. Corundum porphyroblasts and quartz coexist with porphyroblastic almandine-rich garnet, hercynite spinel, ilmenite and magnetite. Corundum and quartz are separated by sillimanite or a composite corona consisting of sillimanite and garnet, whereas corundum shows sharp grain boundaries with spinel, ilmenite and magnetite. Porphyroblastic corundum contains prismatic sillimanite inclusions in which irregularly shaped quartz is enclosed. Two distinct reactions are inferred from the textural features: corundum+quartz=sillimanite and spinel+quartz= garnet+sillimanite. From the petrographical features, we infer that corundum-quartz-garnet-spinel was the peak metamorphic assemblage. Although large uncertainties exist regarding the positions of the respective reactions in P-T space, from several published experimental results and theoretical calculations a peak metamorphic condition of 12 kbar and 1100°C is estimated as the lower stability limit of the corundum-quartz assemblage. Decompression from the peak P-T condition to c. 9 kbar, 950°C is inferred.