Neoproterozoic crustal geodynamics of the Northwest Indian block as revealed in magmatic episodes
Intervenant : Manoj K. Pandit
Department of Geology, University of Rajasthan, Jaipur 302004 (India)
The NW Indian block exposes Grenvillian age to late Neoproterozoic, predominantly granitic, rocks along the western margin of NE-trending Proterozoic Aravalli – Delhi Fold Belt that encompass a critical time interval from Rodinia assembly and breakup. The region hold a position in paleogeographic reconstructions of supercontinent Rodinia and located along its western margin in most paleogeographic reconstructions. The NW Indian block comprises the Archean – Proterozoic Banded Gneiss – Bundelkhan Craton in the east and Neoproterozoic – Pahnerozoic Marwar block in the west, both separated by the NE-trending Proterozoic Aravalli – Delhi Mobile Belt (ADMB). The Marwar Block amalgamated with the ADMB at ~1 Ga and this crustal convergence also initiated ophiolite obduction (Phulad Ophiolite Suite). The ocen floor closure and continent – continent collision event is also manifested in the emplacement of 967 Ma calc-alkaline Sendra Granites. Subsequent tectonomagmatic event, the Erinpura Granite intrusions, spans between 870 – 800 Ma and marks end of the Delhi Orogeny. The most extensive event is the 770 – 750 Ma predominantly felsic magmatism called the Malani Igneous Suite (MIS). The MIS comprise predominantly felsic volcano-plutonic rocks (rhyolite – ignimbrite, peraluminous – perlakaline granites, felsic and mafic dykes). The MIS has been traditionally described either as Anorogenic, rift-related or plume related and more recently as an Andean type event. Recent paleomagnetic data suggest a much northerly paleoposition for the NW Indian block than proposed earlier. End Proterozoic event in this region is the deposition of sand – shale – carbonate sediments of Marwar Supergroup where uppermost unit has been assigned an Early Cambrian age.