Neoarchean–Paleoproterozoic HP-HT metamorphism in the Bhopalpatnam granulite belt, Bastar Craton (India): Insights from phase equilibria modelling and monazite geochronology

Abstract

The Bhopalpatnam Granulite Belt (BGB), located within the southwestern part of the Bastar Craton (India), is composed of granite gneisses with numerous enclaves of high-grade rocks, including quartzofeldspathic gneisses, orthopyroxene-free mafic granulite, and garnetiferous two-pyroxene granulite. In addition, the marginal parts of the belt preserve patches of garnetiferous psammo-pelitic gneisses. New petrographic, metamorphic (conventional and phase equilibria modelling) and monazite geochronological investigations of these high-grade rocks constrain the conditions and timing of granulite-facies metamorphism and enable to demonstrate the tectonometamorphic history of the BGB. The garnet-bearing psammo-pelitic gneisses underwent medium pressure-high temperature (MP-HT) and retrograde metamorphism at P-T conditions of 9.4 ± 1.0 kbar/797 ± 39 °C and 5.1 ± 1.1 kbar/697 ± 69 °C, respectively. The quartzofeldspathic gneisses experienced high pressure-high temperature metamorphism (HP-HT; 12.0 ± 0.9 kbar/785 ± 48 °C), followed by retrogressive cooling at 10.6 ± 0.8 kbar/683 ± 42 °C. The orthopyroxene-free mafic granulites and two-pyroxene granulites witnessed HP-HT metamorphism at 11.0 ± 0.8 kbar/827 ± 45 °C, followed by MP-HT metamorphism at 8.4 ± 0.9 kbar/803 ± 66 °C and retrograde cooling at 5.7 ± 1.5 kbar/555 ± 80 °C. The U–Th–total Pb dating of monazites from the quartzofeldspathic gneiss yielded peak (HP-HT) metamorphic age at 2588–2461 Ma, MP-HT metamorphism at 2499–2308 Ma, and thermal events associated with granite magmatism at 2292–2111 Ma. Based on similar clockwise P–T history and Late Archean-Early Mesoproterozoic tectonothermal events, we suggest that the Bhopalpatnam and Karimnagar granulite belts evolved coherently until the Mesoproterozoic time and eventually rifted apart during the development of the Pranhita-Godavari rift basin between ∼ 1.6–1.4 Ga. The HP-HT and MP-HT granulite-facies metamorphic episodes identified in the BGB are correlated with the continent–continent collision between Bastar and eastern Dharwar cratons.