Inferring a Neoproterozoic orogeny preceding the Rodinia break-up in the Sirohi Group, NW India

Abstract

AbstractRecent studies indicate the Delhi Orogeny to be a Grenvillian-age collision event in the NW Indian Shield. West of the southern part of the South Delhi Fold Belt, aeromagnetic anomalies show a high-angle relationship with the Delhi Fold Belt trend. We examined an argillaceous–calcareous metamorphosed sequence exposed within and adjacent to this aeromagnetic anomaly. This sequence, deposited over a granitic basement, is reported as the Sirohi Group. The basement granite is dated to be 892±10 Ma (Erinpura age) and this was partially reset at 815±43 Ma. The metapelites preserve a low- to medium-grade metamorphic assemblage (peak temperature of c. 460°C) and the metamorphism took place at 822±29 Ma, which was partially reset at 723±65 Ma. The partial resetting can be ascribed to the Malani eruption. Control of accessory minerals on the garnet trace element chemistry is evident in the Y distribution of the two analysed garnets.It is contended that the Rodinia break-up, marked by Malani Igneous Suite, was preceded by an orogenic event (the Sirohi Orogeny) which marked the culminating mountain-building event in the cratonization of the NW Indian Shield.