Search

[Display omitted] • Juvenile crust in Singhbhum Craton formed at ∼3.51, ∼3.45, 3.38–3.25, 3.15–3.05 and ∼2.80–2.75 Ga. • Reworking of older crust in the craton occurred at ∼3.46, ∼3.3, ∼3.1 and ∼2.8 Ga. • Maximum crustal thickness was attained at ∼3.3 Ga followed by a possible reduction over ∼3.1–2.8 Ga. • Paleo-Meso–Archean continental growth occurred through episodic intraplate juvenile magmatism and resultant crustal reworking. The composition of continental crust and its temporal variation, the mechanism of crust-mantle interaction, and the degree of mantle depletion during the early Archean have been widely debated. To address these issues related to the Singhbhum Craton, we present whole-rock sediment geochemistry, detrital zircon U-Pb date, trace element and Hf isotope data from four Archean clastic sedimentary successions. The rocks have high whole-rock K 2 O/Na 2 O, relatively high La and Th compared to Ni and Sc, distinct negative Eu anomaly and flat HREE patterns, and high detrital zircon U/Yb ratios. These features suggest attainment of early crustal stability with the sediments derived from a strongly weathered basement dominated by granitoids formed through shallow intracrustal melting. Detrital zircon U-Pb and Hf isotope data indicate episodic crust formation at ∼3.51, ∼3.46, 3.38–3.25, 3.15–3.05 and ∼2.80–2.75 Ga. Each major crust formation event is marked by addition of depleted mantle-derived juvenile crust and its quick reworking. Besides, episodic tapping of older crust, as indicated by a wide range (both positive and negative) of zircon εHf t values, are evident at ∼ 3.46, ∼3.3, ∼3.1 and ∼2.8 Ga. Pressure-sensitive zircon trace element ratios suggest that the crust attained the maximum thickness at ∼3.3 Ga followed by a possible reduction in thickness over ∼3.1–2.8 Ga. In the absence of strong evidence of subduction, the rock association and their temporal distribution (coeval granitoid and mafic-ultramafic magmatism) suggest that the Paleoarchean-Mesoarchean crustal growth in the Singhbhum Craton was a result of episodic, depleted mantle-derived, intraplate magmatic injection and attendant crustal reworking. [ABSTRACT FROM AUTHOR]

• Granitoids of Singhbhum Craton. • Two generation of TTGs at 3.42 and 3.32 Ga formed by melting of juvenile mafic crust. • Later K-rich, silicic granites at 3.28 and 3.25 Ga formed by melting of tonalites. • Recurring crustal melting in a gradually thickening oceanic plateau. • Final cratonisation of the Singhbhum Craton at 3.25 Ga. A significant part of many Archean cratons formed during Paleoarchean. Yet, the mechanism and tectonic setting of formation of Paleoarchean continental crust remain highly debated. In this contribution, we present field, petrographic, geochemical, zircon U-Pb age and Hf isotope data on Paleoarchean granitoids from west-central part of the Singhbhum Craton (Champua-Hat Gamharia corridor), India. The whole process starting from nucleation of a juvenile continent to its evolution and final stabilization is documented. The core of the craton nucleated with formation of 3.45–3.40 Ga TTGs showing juvenile character (zircon ɛHf t = +0.6 to +7.1). These rocks show slightly depleted HREE and Y, negligible Eu-anomaly (Eu/Eu* = 0.90 to 1.00) and moderate Sr/Y (25–64), consistent with derivation from a low-K mafic crust at a pressure near the lower end of the garnet stability field, causing subordinate garnet retention in the residue and negligible role of plagioclase. A second generation of TTG formation took place at 3.32 Ga in the area by deeper melting of a juvenile mafic crust (zircon ɛHf t = +1.3 to +5.7) as suggested by strongly depleted HREE and Y, and high Sr/Y (52–155) implying significant amount of garnet retention in the residue. Subsequently, the area witnessed intracrustal melting at 3.28 and 3.25 Ga which tapped moderately old to juvenile (zircon ɛHf t = −1.9 to +4.5), mostly TTG sources at variable depths generating potassic, LILE-enriched, high-silica granites. Intrusion of these potassic granites marks the final cratonization of the Singhbhum Craton. The sequence of events is interpreted in terms of repeated crustal melting and granitoid generation in a gradually thickening oceanic plateau with a progressive change in granitoid source from mafic to felsic in composition. A synthesis of rock assemblage, regional geological setting and structural pattern also supports intraplate nature of the magmatism in Singhbhum Craton, which might have been a significant mechanism of crustal growth worldwide during Paleoarchean. Further, a comparison of juvenile crustal growth and crustal reworking events of the Singhbhum and other Indian cratons show that these cratons record distinct evolutionary histories and were probably nucleated at different sites. [ABSTRACT FROM AUTHOR]