Neoarchean–Paleoproterozoic stratigraphy of the Dhanjori basin, Singhbhum Craton, Eastern India: And recording of a few U–Pb zircon dates from its basal part

Abstract

The stratigraphy of the Dhanjori basin placed at the northeastern margin of the Paleo-Mesoarchean Singhbhum Craton has been revised. A mainly quartz-pebble conglomerate (QPC) and volcani-clastics bearing unit at the base of the Dhanjori basin and intruded by the Mayurbhanj Granite, has been named Phuljhari Formation. The Dhanjori volcani-sedimentary sequence with quartzite–polymictic conglomerate at its base, disconformably overlies the Phuljhari Formation and non-conformaby over the Mayurbhanj Granite. The Dhanjori Group is inferred to broadly range in age from 2.6–2.1 Ga. Detrital zircons from QPC belonging to the Phuljhari Formation have yielded oldest chemical ages of 3.09–3.04 Ga thus fixing the upper age limit of the formation. The 3.09 Ga old zircons recovered earlier from the Mayurbhanj Granite, which is intrusive into the relatively younger Phuljhari Fm., therefore appears to be xenocrystic in nature. A fine grained variety of the Mayubhanj Granite, close to its intrusive contact with the Phuljhari Fm., was sampled during the present study. It has recorded strong impress of acid magmatic event around 1.0–0.8 Ga by its lower intercept and an upper intercept age of ∼2.8 Ga. The latter might record the inherited age of protolith to the Mayurbhanj Granite and correspond to widespread granite magmatic activity affecting the margin of the Singhbhum Craton. Signature of 1.0–0.08 Ga old thermal perturbation also affected lower parts of the Dhanjori basin and the Singhbhum Shear Zone. Detrital Au–U bearing QPC in the Phuljhari Formation represent Neoarchean sedimentation at the margin of the peneplained craton. The Dhanjhori Group comprising mafic–ultramafic volcanics and siliciclastics was hosted in rift induced intracratonic basin around Neoarchean–Palaeoproterozoic threshold.