Recent 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.
Chemical Th-U-total Pb method of dating monazite by an Electron Probe Micro Analyzer (EPMA) is a well-known technique for constraining chronology of geological events. In this communication, the analytical conditions of monazite dating using SXFive EPMA recently installed at the Department of Geology, Banaras Hindu University is reported. Consistency in the geochronological data of the monazites from the geochronologically well-constrained high grade metamorphic terrain of Bundelkhand craton, north central India, confirms the reliability of the BHU-EPMA facility for the U-Th-Pb geochemical dating of monazite.
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