Magmatic evolution of mafic granulites from Anakapalle, Eastern Ghats, India: implications for tectonic setting of a precambrian high-grade terrain

Abstract

Mafic granulites showing intrusive relationships with enclosing pelitic, calcareous and quartzofeldspathic gneisses at Anakapalle, Eastern Ghats belt, share a common retrograde metamorphic history (decompression followed by near-isobaric cooling) and are, therefore, considered to be syn-metamorphic. Detail textural, phase chemical and bulk chemical analyses of the mafic granulites show that (a) these are melts derived through fractionation of a primary tholeiitic magma and (b) they crystallized at temperatures <1000°C and were thus in thermal equilibrium with the country rock granulites during peak metamorphism. Comparison with experimental data on similar bulk compositions constrains the depth of emplacement of the magmas at 30–35 km. Geochemical characteristics indicate that the mafic magmas are essentially similar to continental flood basalts and have thus been generated in an extensional set-up. The apparent clockwise trajectory recorded in the Anakapalle granulites was produced by extension of the crust of near-normal thickness with concommitant basic magmatism.