Neoproterozoic crustal evolution of northwestern Indian Shield: Implications on break up and assembly of supercontinents

The Neoproterozoic geological history in western Rajasthan, northwest India n Shield began with the intrusion of anorogenic bodies of diorites at ca. 1 000 Ma. Recently available single zircon dates indicate possible continuity of the "Grenville belt" beyond Eastern Ghats through the Satpura Orogenic Belt into the Aravalli Mountains. Closely following this tectono-thermal ev ent at the Meso-Neoproterozoic boundary, some narrow basins opened west of the Aravalli Mountains. The basin closing related to the tectonic inversion and associated magmatism at ca. 835 Ma completed the cratonisation process of the Precambrian Aravalli crust. Subsequent geological events witnessed over a wide region to the southwest of the Aravalli Mountains, were in the form of "plume-related" magmatism of the Malani Group, which comprises bimo dal Volcanics (dominantly felsic and minor mafic), minor sediments, and per aluminous and peralkaline granitoids. An unconformity indicating a hiatus i s noticed at the base of the Malani Group. The final phase of the Neoproter ozoic cratonic history is associated with thick platformal deposits of the Marwar Supergroup. The Marwar basins show a clear sedimentological affiliat ion with the sub-Himalayan basin of "Saline Series" in Pakistan. The beginning of the Neoproterozoic history in the northwestern Indian Shie ld is correlated with the events related to the possible break up of the Ro dinia Supercontinent. Much of the later phases of the Neoproterozoic geolog ical events witnessed in the Indian Shield are traditionally described as t he "Pan-African". However, the geological events recorded in the northweste rn part of Indian Shield are neither strictly coeval nor are tectonically c orrelatable with the 'orogeny and fabric-forming contemporary events' of th e East African Orogeny (EAO), which is undoubtedly the type terrane of the Pan-African Tectono-thermal Belt. The evolution of the northwestern Indian Shield during the Neoproterozoic does not appear to be related in any way w ith the Pan-African events observed in EAO. Further, the most talked about 'Pan-African' dates at ca. 500+/-50 Ma, are manifestations of anorogenic th ermal event, which possibly marks an aborted attempt to fragment the 'Great er Gondwana' during the early Palaeozoic.