Evolution of the Singhbhum Craton and supracrustal provinces from age, isotopic and chemical constraints
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© 2019 Elsevier B.V. The Singhbhum Craton and supracrustal provinces in eastern India are one of a few Precambrian terranes that record protracted sedimentation and magmatism spanning the Paleoarchean to Neoproterozoic. A paucity of robust geochronological and isotope geochemical data and the perpetuation of poor-quality data have hampered petrogenetic interpretations, and regional and global tectonic correlations. Here, we report new zircon U–Pb and Hf isotopic data, and new muscovite 40Ar/39Ar data from key stratigraphic intervals in the Archean nucleus and the North Singhbhum Mobile Belt. Together with critical scrutiny of available geochronological data, it is clear that the Older Metamorphic Tonalite Gneiss (with several Hadean zircon xenocrysts), the Older Metamorphic Group and parts of the Iron Ore Group were contemporaneous at ca. 3510–3375 Ma. Zircon Hf and whole-rock Nd data from these units reveal juvenile but also subchrondritic values that suggest crustal recycling operated in the Hadean and early Archean. Continued juvenile magmatic addition and crustal reworking of older portions of the craton led to the progressive emplacement of the Singhbhum Granite at ca. 3365–3285 Ma. Minor Meso- to Neoarchean granitoid emplacement, mafic dyke swarms and sedimentation completed the building of the Archean nucleus. In the early Proterozoic, supracrustal deposition and magmatism of the poorly temporally-constrained Dhanjori and Chaibasa Formations occurred along the northern margin of the craton, and equivalent units along the southern margin in the Rengali Province. In the North Singhbhum Mobile Belt, a major hiatus then occurred. Deposition and emplacement of the conformable Dhalbhum, Dalma and Chandil Formation followed, with zircon U–Pb data of 1629 ± 4 Ma from rhyolite flows in the lower Chandil Formation providing a maximum age for the underlying formations. Detrital zircon from three samples in the Dhalbhum and Chandil Formations reveal equivalent zircon populations, where >65% are juvenile to moderately evolved ca. 2550–2430 Ma grains, with additional 2800–2600 Ma, 2150–1950 Ma and ca. 1750 Ma subpopulations. Provenance for these samples is probably predominantly from the Dharwar ± Bastar Cratons to the southwest. In a tectonic context, arc-related orogenesis at ca. 1.6 Ga started from the southern tip of India and propagated northwards to the Singhbhum Craton to explain derivation of detritus from the topographically-higher Dharwar ± Bastar Cratons. Slab roll-back induced separation in the Mesoproterozoic before final re-amalgamation at ca. 1.0 Ga is evidenced by widespread Grenvillian-aged magmatism, metamorphism and deformation in Peninsular India, including syenitic rocks in the Chandil Formation, zircon Pb-loss recorded in other samples and a muscovite 40Ar/39Ar age along the Singhbhum Shear Zone of 970 ± 8 Ma. No further tectonothermal or magmatic activity is known in the Singhbhum Craton or supracrustal provinces, attesting to its final stabilization in the earliest Neoproterozoic.
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