Geochronological Constraints on Evolution of Singhbhum Mobile Belt and Associated Basic Volcanics of Eastern Indian Shield

Abstract

The Singhbhum Mobile Belt (SMB) of the eastern Indian shield represents a roughly east-west-trending arcuate belt of folded supracrustals overlying the granite-greenstone basement of the Singhbhum-Orissa Craton along its northern, eastern and western margins and is bounded by the Chotanagpur Gneissic Complex to further north. The radiometric ages of the basement Singhbhum and equivalent granites and the intrusive anorogenic Mayurbhanj granite pluton constrain the time of evolution of this mobile belt between ∼3.12 and 3.09 Ga. Hence, the SMB supracrustals also known as Singhbhum Group, is late Mesoarchaean in age and not Proterozoic as thought earlier. The evolution of the SMB was followed by emplacement of some major basic igneous rocks within or adjacent to the supracrustals. These include Simlipal volcanics at ∼>3.09 Ga on the SMB, Mayurbhanj gabbro along with Mayurbhanj granite at ∼3.09 Ga along the marginal part of the craton near the SMB, and the Dalma volcanics on the SMB along with the Dhanjori volcanics adjacent to SMB at ∼2.80 Ga. The ∼ 2.80 Ga old basic volcanics is also associated with emplacement of some small granite plutons occurring along the marginal part of the craton, one of them, the Tamperkola granite intrudes the SMB. The ∼>3.09 Ga onward igneous activities along the marginal part of Singhbhum-Orissa Craton took place essentially under anorogenic tectonic setting before being affected by a major metamorphism at ∼2.50 Ga, which is recorded on the Dalma volcanics and on some small granite pluton occurs along the marginal part of the craton. The Jagannathpur and stratigraphically equivalent Malangtoli volcanics, occurring within the Singhbhum-Orissa Craton at the west, were erupted at ∼2.25 Ga. The boundary between the SMB supracrustals and the Singhbhum-Orissa Craton is demarked by a prominent shear zone known as the Singhbhum Shear Zone, which shows multiple reactivation, the oldest being at ∼3.09 Ga, followed by subsequent reactivation during Palaeo- and Mesoproterozoic periods at ∼2.2, 1.8, 1.6-1.5, 1.4 and 1.0 Ga respectively. The Singhbhum Group and the adjacent Chotanagpur Gneissic Complex appear to have evolved from a near shore syn-rift and a distal post-rift stable shelf sedimentary assemblages respectively, which were deposited without any stratigraphic break in a marine basin existed in the present north of the Singhbhum-Orissa Craton. Both of these assemblages were deformed and metamorphosed together during Proterozoic at ∼2.5 to >2.3 Ga, ∼1.6 Ga and ∼1.0 Ga.