Provenance of >2.8 Ga Keonjhar Quartzite, Singhbhum Craton, Eastern India: Implications for the Nature of Mesoarchean Upper Crust and Geodynamics

We determined the provenance, tectonic setting, and weathering characteristics of weakly metamorphosed Mesoarchean siliciclastic rocks from the Singhbhum craton, eastern India, on the basis of their petrographic and geochemical compositions. The 1.5-km-thick siliciclastic succession, formally introduced here as the Keonjhar Quartzite, unconformably overlies the Singhbhum Granite (3.1-3.4 Ga) and has been assigned a Mesoarchean depositional age on the basis of a youngest detrital zircon of 3.01 Ga and intrusive granitoids with ages of not less than 2.8 Ga. Their highly matured and recycled nature is reflected in several geochemical proxies. The highly variable chemical index of alteration (CIA) values and the pattern in the A-CN-K plot indicate variable degrees of weathering, which in turn suggest non-steady-state weathering conditions. The high CIA values also suggest a stable tectonic setting that caused the erosion rates to decrease, which in turn caused a rise in the flux of weathered materials. The A-CN-K plot suggests sediment derivation predominantly from granodioritic and mafic rocks. Quartz grains with abraded overgrowth, abundant pseudomatrix, the presence of metasedimentary rock fragments, and variation in Zr/Sc support the presence of recycled source. The trace element compositions are consistent with a mixed source with differentiated felsic upper continental crust (UCC) as well as a more primitive mafic source. In significant contrast to most post-Archean greenstone successions, the rocks here display rare earth element patterns similar to those of the post-Archean shales. Recycling and intracrustal fractionation processes imply craton stabilization and confirm the existence of a Mesoarchean continental crust comparable to the post-Archean UCC. Here we infer amodern-day-like intracratonic setting for this succession on the basis of the geochemical fingerprints. The sandstone composition provides evidence in favor of modern-style plate tectonics during the Mesoarchean.