NEORPROTEROZOIC ACID MAGMATIC EVENTS IN THE NW INDIAN CRATON AND THEIR SIGNIFICANCE IN RODINIA DISPERSAL

Neoproterozoic acid magmatic events in NW India are unique in terms of diversity in tectonic setting despite a close temporal and spatial association. The Sendra granitoids (intrusive into the metasediments of Delhi Supergroup) are tonalitic to granodioritic in composition, however, the predominant component is essentially granitic (granite gneiss) which has yielded a U – Pb zircon age of 967 Ma and seems to be related to the 1 Ga collisional event. A younger event comprises of variably deformed granodiorite – tonalite – granite to granite gneiss, popularly known as Erinpura Granite. The granite gneiss component has yielded 830 Ma age and has been considered to mark the end of Delhi orogeny. The most voluminous of the Neoproterozoic acid magmatic events, Malani Igneous Suite, is characterized by an initial felsic (bimodal at places) volcanism followed by emplacement of granites and acid to basic dykes. These rocks are undeformed and unmetamorphosed and show well-documented intrusive relationship with the older Delhi metasediments and Erinpura granite. Occurrence of conglomerate units and their linear disposition suggest that the volcanic activity took place along roughly N – S and subparallel fracture systems. The Sindreth bimodal volcanics which have long been considered as part of Delhi Supergroup are undeformed and show resemblance with Malani rocks. The U - Pb zircon ages indicate a 20 Ma span for Malani felsic volcanics and granites ( 770 – 750 Ma). The acid magmatic events in NW India appear to be the manifestation of amalgamation of Rodinia at ~1 Ga and its breakup at ~750 Ma. The 770 -750 Ma Malani magmatism (non orogenic) appears to be consistent with coeval events recorded in Seychelles and Madagascar, substantiating their spatial association prior to Gondwanic break-up. The trio formed the western margin of the Rodinia which also raises the possibility of a ‘subduction’ setting for the Malani magmatism.