Abstract:
In significant contrast to other cratonic blocks of India, the Singhbhum cratonic successions record contin-uous depositional record from the Palaeoarchaean to Mesoproterozoic. Although the sedimentary faciescharacteristics and mode of stratigraphic sequence building of the Dhanjori and Chaibasa Formations arewell known, sedimentary geochemistry, provenance and tectonic milieu of deposition of these two for-mations are hitherto unknown. The current manuscript presents geochemical and Sm–Nd isotopic datafrom the Dhanjori and Chaibasa Formations for the first time and combine previous sedimentological datawith the goal to expand the framework for understanding the depositional and tectonic setting of thesetwo formations. The Sm–Nd isotopic data for the Chaibasa clastics is unambiguous with respect to proven-ance. Average εNd(t = 2.2 Ga) = −0.8 ± 1.0 and average Nd model age (TDM) = 2.51 ± 0.08 Ga with average147Sm/144Nd ratios = 0.1114 ± 0.0041 for phyllites and quartzites indicate an extremely homogeneoussource signature consistent with a late Archaean “juvenile” crustal provenance, possibly a dominantlyupper crustal provenance. The Sm–Nd isotopic data from the older Dhanjori Formation also indicatebroadly similar provenance as comparable lithologies in the younger Chaibasa Formation. Our Sm–Ndisotopic data is entirely consistent with the previous sedimentological data and confirms a terrestrial, rift-dominated tectonic setting for the Dhanjori Formation (proximal sources, poorly mixed provenance) anda marginal marine to offshore setting for the more homogeneous Nd isotopic signature of the ChaibasaFormation (distal sources, well mixed provenance).
