Precambrian Chronostratigraphic Growth of Singhbhum-Orissa Craton, Eastern Indian Shield: An Alternative Model

The Precambrian granite-Greenstone terrain of eastern Indian shield includes Singhbhum-Orissa craton, Singhbhum Mobile Belt supracrustals (Singhbhum Group) along its northern, eastern and western margins, and Chotanagpur Gneissic Complex towards further north. Recent isotopic ages along with other geological considerations show that these three crustal units perhaps constitute a single cratonic block, which grew in sequence from -3 55 to 1 00 Ga. The center of crustal growth gradually migrated with younging from the present south to north. Prior to the onset of this crustal growth, there was a still older crust in this region at -3 60 Ga, the remnants of which are preserved only as detrital zircons at present. However, the Singhbhum-Orissa craton represented the nucleus of the presently existing cratonic block, which had formed between -3 55 and 3 12 Ga through two successive supracrustal-granite cycles, well separated by an erosional unconformity. The first cycle included Older Metamorphic Group supracrustals, Older Metamorphic Tonalite Gneiss and Singhbhum Granite, phase-I, Singhbhum Granite, phases II, Chakradharpur Granite Gneiss and Nilgiri Granite that grew in sequence from -3 55 to 3 30 Ga. The second cycle included Iron Ore Group supracrustals followed by emplacement of Bonai Granite and Singhbhum Granite, phase III, and had an evolutionary history ranging from -3 30 to 3 16 Ga or up to -3 12 Ga. The supracrustal-Granite cycles began with formation of supracrustal sequences in anorogenic setting, followed successively by major folding during following orogeny and final emplacement of orogenic granites into these deformed supracrustals. The emplacement of anorogenic Mayurbhanj Granite pluton with Mayurbhanj Gabbro along the northeastern margin of the craton at -3 09 Ga marked the stabilization of Singhbhum-Orissa craton. Emplacement of Singhbhum Granite, phase II, Singhbhum Granite, phase III and Mayurbhanj Gabbro recorded metamorphism on the older rock units of Singhbhum-Orissa craton. In the late Meso- to Neoarchaean period Singhbhum-Orissa craton grew along its northern, western and eastern margins by formation of a supracrustal sequence of syn-Rift nature including mostly clastic sediments and minor basic and acid volcanics, which followed upward by major basic volcanisms. These supracrustals included Singhbhum Group, which unconformably overlay the Singhbhum Granite, phase-III and equivalent granite basements and was subjected to two major phases of folding, before being overlain by undeformed. Simlipal volcano-Sedimentary basin occurring at the eastern part of the craton. The evolution of Singhbhum Group and Simlipal basin took place between -3 12 and 3 09 Ga, before being intruded by anorogenic Mayurbhanj Granite( -3 09 Ga) and was followed by the formation of overlying riftogenic Dalma Group and adjacent Dhanjori Group of basic volcanics and some minor acid plutonics at the marginal part of the craton at -2 80 Ga and their subsequent major metamorphism at -2 50 Ga. A critical review of present available geological and radiometric age data suggests that Chotanagpur Gneissic Complex was evolved from a supracrustal precursor, some of them were formed at least before -2 3 Ga. The Singhbhum Group supracrustals and adjacent Chotanagpur Gneissic Complex perhaps had evolved from a common sedimentary precursor along with volcanics, which were deposited in a marine basin that existed at the present north of Singhbhum-Orissa craton during late Mesoarchaean period. The syn-rift sedimentary assemblage of the Singhbhum Group was deposited along the margin of Singhbhum Orissa craton, whereas the post-rift stable shelf sedimentary precursor of the Chotanagpur Gneissic Complex was deposited towards further north. In the Neoarchaean period between - >3 09 Ga and -2 5 Ga the nature of deformation along the marginal part of Singhbhum-Orissa craton was extensional type. In the following Palaeo- to Mesoproterozoic period, the protolith of Chotanagpur Gneissic Complex grew in sequence between - > 2 3 and 1 0 Ga through two time-Separated supracrustal granite cycles where the first and second cycles ended at -1 60 and 1 00 Ga respectively. Radiometric ages suggest that Chotanagpur Gneissic Complex along with Singhbhum Group experienced major magmato-metamorphic activities during Palaeo- and Mesoproterozoic periods at -2 5 or >2 3 Ga, 1 6 Ga, 1 0 Ga and 0 9 Ga. During this period Singhbhum-Orissa craton recorded basic volcanism (Jagannathpur and possibly Malangtoli Volcanics) at -2.25 Ga, followed by deposition of clastic sediments (Kolhan Group) and finally emplacement of mafic dykes and sills (Newer Dolerite) in three successive sequences at -2.0 Ga, 1.6 Ga and 1.0 Ga, where all these phenomena took place under anorogenic setting. The Singhbhum Shear Zone, which marked a tectonic boundary between Singhbhum-Orissa craton and Singhbhum Mobile Belt to north, was reactivated several times during geological past, the oldest being at -3.09 Ga, followed by emplacement of Soda Granite pluton along this shear zone at -2.22 Ga, copper mineralization at -1.77 Ga, shearing at - 1.67-1.63 Ga, uranium mineralisation at -1.58- 1.48 Ga and the final phase of shearing at - 1.0 Ga.