LAUSR

Abstract Paleoproterozoic mobile belt of Eastern India well known as Singhbhum Mobile Belt (SMB) bears the evidences of tectono-magmatic processes and crustal evolution like many other major Precambrian terrains of the world. Because of some significant major stratigraphic, structural, geochemical and isotopic constraints SMB could not considered as plume related continental rift basin as proposed by earlier workers. Geological evidence in favor of global melting events at 2.7 and 1.9 Ga are absent. TTG-type 3.5 Ga old gneisses (OMTG) and volcanic arc / syn-collision geochemical signatures of 3.2-3.4 Ga old Singhbhum Granitoid Complex (SBGC) occurring in the south of Singhbhum Shear Zone (SSZ) suggest that on the regional scale plate-tectonic processes were operational during Mesoarchean or slightly earlier. Lack of K-rich granites, a characteristic feature of Neoarchean suggests that cratonization in the Singhbhum Proto-continent did not complete till the end of Archean at 2.5 Ga. Flysch-type characters of Chaibasa Formation imply an early syn-orogenic evolution of the metasediments. Subduction zone geochemical characteristics of Ongarbira and Dhanjori metavolcanic rocks further corroborate plate convergence. Dalma metavolcanic rocks have an unconformable relationship with the underlying Dhalbhum Formation. Available radiometric age data from SMB (2.8 to 1.0 Ga) suggests that there is no tectonic or metamorphic discontinuity across the SSZ but the contact of SMB supracrustal rocks with SBGC marks out a tectonic and metamorphic break. Structural evidence indicates that SSZ came into existence quite early in the orogenic history perhaps around 2.6 Ga and there have been later reactivations up to 1.0 Ga.