A better understanding of Archean crustal evolution: exploring the sedimentary archive of the Singhbhum Craton, eastern India

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 K2O/Na2O, relatively high La and Th compared to Ni and Sc, distinct negative Eu anomaly and flat HREE pat-terns, 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 & epsilon;Hft 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.