Abstract Understanding the evolution of the Chotanagpur Granite Gneiss Complex (CGGC) of the East Indian Shield is crucial to decipher the role of the Indian Shield in the formation of the Rodinia supercontinent. The area around Deoghar–Dumka exposes a suite of granulite-facies orthogneisses (variably retrogressed to amphibole–biotite gneiss) that enclose remnants of Palaeoproterozoic metasedimentary and meta-igneous rocks. Results from mineral chemistry, laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) U–Pb dating of zircon and limited bulk-rock compositions of the studied rocks suggest that the magmatic protoliths of the felsic orthogneisses had A-type chemistry, and that these were emplaced at approximately 1450 Ma presumably in a continental rift setting. Intense deformation and metamorphism of the felsic rock culminated at approximately 9 kbar and 850°C along an apparent geothermal gradient of 26°C km −1 . These peak metamorphic conditions were successively followed by initially a steeply decompressive and then a weakly decompressive retrograde pressure–temperature path. The shape of the retrograde pressure–temperature path and the estimated geothermal gradient at the metamorphic peak are interpreted to be the products of continent–continent collision; U–Pb dates of metamorphic zircon overgrowths suggest an age of approximately 943 Ma for the collisional event. This study demonstrates that ‘Grenville-age’ orogenesis thoroughly reworked the approximately 1450 myr-old basement of the CGGC during the formation of the Rodinia supercontinent.

Abstract The Central Indian Tectonic Zone (CITZ) marks the suture zone where the North and South Indian cratonic blocks amalgamated to form the Greater Indian Landmass (GIL). It consists of three broad domains from west to east: the central CITZ occupying the central region of mainland India juxtaposed between two mobile belts, namely the Sausar Mobile Belt (SMB) in the south and the Mahakoshal Mobile Belt (MMB) in the north; the Chotanagpur Granite Gneiss Complex (CGGC) lying east of the main CITZ; and the easternmost Shillong Plateau Gneissic Complex (SPGC). The studied granites are from the Bathani Volcano Sedimentary sequence (BVSs) from the northern margin of the CGGC. These are high-K, calc-alkaline, I-type granites related to arc magmatism and are interpreted to have formed by partial melting of an igneous source at upper-crustal depths. The granitic magma underwent extensive fractional crystallization of plagioclase, biotite, K-feldspar and ilmenite during emplacement. The U–Pb (ID-TIMS) zircon emplacement age is c . 1.7–1.6 Ga for these granites. This episode of magmatism can be correlated to the global event of the Nuna supercontinent assembly also reported from the MMB of the central CITZ. We infer that the BVSs is the eastern continuation of the MMB of the central CITZ.

Abstract Geological information on the Chotanagpur Granite Gneiss Complex (CGGC) has been reviewed with a view to: (a) identifying the different metamorphic episodes; (b) developing an event stratigraphy in the high-grade blocks; and (c) correlating the different metamorphic episodes with the globally extensive orogenic processes. Integrating the existing geological information, the geological evolution of the high-grade block of the CGGC has been divided into four stages associated with four distinct metamorphic events ( M I − M IV ). The earliest metamorphic event ( M I ) that is recorded in granulite enclaves in the regionally extensive felsic gneisses culminated in ultrahigh temperatures (>900 °C at c . 5–8 kbar) at around 1.87 Ga. In the second stage, voluminous felsic magmas were intruded – the M I granulites – and were metamorphosed to form migmatitic felsic gneisses ( M II ) within about 1.66–1.55 Ga. The third stage witnessed intrusions of a suite of anorthosite and porphyritic granitoids ( c . 1.55–1.51 Ga), followed by high-grade metamorphism (700±50 °C, 6.5±1 kbar, M III ) during approximately 1.2–0.93 Ga. The fourth stage ( M IV ) is marked by the intrusion of a suite of mafic dykes, followed by infiltration-driven metamorphism (600–750 °C at 7±1) during 0.87–0.78 Ga. The proposed metamorphic events have been correlated with the supercontinental cycles in the Proterozoic time.