Evolution of the Eastern Ghats Belt, India: A Plate Tectonic Perspective

The Proterozoic Eastern Ghats Belt (EGB) along the east coast of India exposes deep segments of the continental crust, and is considered as a deeply eroded remnant of the present-day Himalayan-type setting. The EGB registers crustal growth of the Indian plate on its eastern side. Precambrian sutures in this poly-metamorphosed and multiply-deformed belt are recognized by the presence of ophiolites (containing unequivocal sheeted dykes and plagiogranite), shear zones, ultrahigh-T metamorphism, massif-type anorthosites and more significantly, by the presence of deformed alkaline rocks and carbonatites (DARCs). The southern segment of the EGB, around Kondapalli (Andhra Pradesh), records the entire gamut of processes from Palaeoproterozoic rifting to Grenvillian/Pan-African collision. The first convergence event that operated between 2 and 1.6 Ga is yet to be identified in other parts of the EGB. The mafic and felsic granulites of Kondapalli exhibit trace element characteristics typical of subduction-related magmatic arcs and the Kondapalli Layered Complex (KLC) is construed as an arc-root complex in the deeply eroded Eastern Ghats orogen. We postulate that the evolution of the EGB involved two distinct episodes of convergence, both being initiated by the onset of continental rifting. In our favoured model, the first rifting event at ~ 2.0 Ga along the eastern margin of the Indian plate, initiated the formation of an Atlantic-type continental margin, which was later converted into an Andeantype continental margin by convergent plate motion at ~1.85 Ga. Final culmination by continent-continent collision was possibly completed by 1.55 Ga. The second episode of rifting between 1.5-1.35 Ga, along the eastern margin of the thickened arc crust, facilitated the emplacement of alkaline rocks and carbonatites (ARCs). The exact timing of the Mesoproterozoic basin inversion and conversion of ARCs into DARCs - either during Grenvillian or Pan-African orogeny - remains elusive.