Occurrence of sapphirine-bearing granulites from Kothuru, Eastern Ghats Mobile Belt: implications on ultra-high temperature metamorphism

In this study, we present evidence for the stable coexi­stence of sapphirine + quartz and the compositional characteristics of the sapphirine-bearing granulites from Kothuru in the Eastern Ghats Mobile Belt (EGMB), India. The study area is an integral part of the Precambrian terrane in the western part of EGMB and is characterized by the granulite facies rocks comprising mainly of pelitic granulites such as charnockites, enderbites, leptynites, khondalites and gneisses, and sapphirine–spinel–quartz-bearing rocks. The chemistry of the minerals present in the assemblage has been examined using the electron probe micro analyser to infer their occurrence and distribution in various reaction textures observed during the petrographic study. The peak and post-peak history of the sapphirine-bearing granulites of Kothuru section have been constrained in the NCKFMASHTO system showing decompressional P–T path of high-grade metamorphic rocks through the intersection of the isopleth contours of various mineral phases present. The proposed P–T path with a steep isothermal decompression retrograde trajectory may be attributed to the over-thrust processes. The results obtained from the petrographic study of the mineral assemblages along with their textural relationship, mineral chemistry, especially Fe3+/FeTotal ratio and pseudosection modelling reveal that the studied segment has arrested promising ultra-high temperature metamorphic signatures and is tectonically distinct from those reported in the adjacent areas.