Archean Charnockites and their supercontinent connection: A case study from the Neoarchean Granulite Eastern Dharwar Craton in South India

The Singhbhum, Bastar, and Dharwar cratons in the South India Block (SIB) form a continuous mass of >2.5 Ga crystalline rocks in South India. In this contribution, we investigate whether these cratons grew together with the suggested ‘Ur’ framework or if they evolved separately. The Karimnagar granulite belt on the NE edge of the Eastern Dharwar Craton (EDC) contain enclaves of mafic granulites and high-Al metapelites within variably deformed charnockites and blastoporphyritic granitoids. The foliated charnockites exhibit magmatic flow texture, euhedral-subhedral pyroxene phenocrysts, and chess-board twinning in the quartz grains. Feldspar and pyroxene phenocryst laths share high-energy boundaries with quartz and each other. The Al-in-Opx thermometry indicates charnockites emplaced at a temperature > 900 °C. Also, the charnockites' whole rock chemistry supports an arc origin. The charnockites' oscillatory-zoned magmatic cores survive the recrystallization of zircon grains. The U-Pb Concordia plot shows a concordant age of 2680±15 Ma and 2504±12 Ma, from magmatic zircon cores. Recrystallized zircon grains exhibit an upper intercept age between 2510±4 Ma and 2509±3 Ma, overlapping with the U-Th-Pb ages in monazites (2502 -2508 Ma). The ²⁰⁷Pb/²⁰⁶Pb age versus εHf(t) plot of zircons indicates that ~2.5 Ga magmatic charnockites originated from <3.0 Ga crustal sources. In contrast, the charnockites from the Bastar craton, exhibit U-Pb ages at 2500 Ma and 1600 Ma. The orientation of structural data, thermometry, and geochronology of the charnockites, when combined together with the existing literature, i.e., lack of 1600 Ma ages from Karimnagar Charnockites, indicate late Neoarchean magmatic charnockites at the EDC margin were formed during a 2.7–2.5 Ga amalgamation between the separately evolved crustal blocks within the Dharwar Craton, probably as a part of Kenorland assembly. Our result is contrary to the concept that the Neoarchean Karimnagar Charnockites were part of a coherently evolved landmasses involving Dharwar and part of Bastar Craton, known as DHABSI, within the Ur supercontinent, that assembled during the Paleo/Mesoarchean evolutionary history of the Earth.