An ensemble of metasediments and gneissic rocks, commonly known as the Jutogh Group and Wangtu Gneissic Complex (WGC), respectively, occur as a tectonic window in the Lesser Himachal Himalaya, India. In the Jutogh Group, chlorite-mica schist, garnet-staurolite schist, and sillimanite-schist develop sequentially, near Jhakri thrust in the west to Wangtu in the east. Phase equilibria modelling implies chemically zoned garnet developed at 550°C to 650°C, 0.8 to 1.0 GPa, destabilising low-temperature assemblages. The retrograde segment consists of exhumation and cooling, resulting in a tight clockwise P-T path. The ɛNd[1.8Ga] of the Jutogh group varies between − 0.97 to − 8.14, with depleted-mantle-model ages between 3.07 Ga to 2.28 Ga. A combination of the isotopic composition of the garnet core and its leachates yields an Sm-Nd isochron age of 472 ± 26 Ma. The combination of the isotopic composition of the biotite, garnet rim, and garnet rim leachate fraction provides an isochron of 453 ± 6 Ma. Textural observations and Insitu U-Th-Pbtotal chemical ages indicate that the metasedimentary rocks contain Cambrian monazites. These monazites exhibit an age cluster around ~ 500 Ma. When combined, the results of phase equilibria modeling, Sm-Nd, and Monazite geochronology imply that the Jutogh Group metamorphosed during Cambro-Ordovician period between India and East Asian Cratons (EAC).
This communication reports novel geochemical and geochronological data of granite from the southeastern part of the Bastar Craton, Central India. The studied samples are leucocratic in appearance and composed of quartz, K-feldspar, plagioclase feldspar, and biotite in decreasing order of abundances. Apatite, sphene, and zircon occur as accessory minerals. The SiO2 and Al2O3 content of the studied sample varies between 61 and 69 wt.% and 13 and 15 wt.%, respectively. The alkali oxides, K2O, and Na2O content ranges between 3 and 6 wt.% and 2 and 3 wt. %, respectively. In the primitive mantle normalized spider diagram, the granites exhibit a negative Nb–Ti, Sr anomaly, and a positive Pb–Th anomaly. Similarly, in the REE normalized spider plot, the granites exhibit a strongly fractionated trend La/YbCN=10.90−28.4 with a negative Eu anomaly (0.42-0.70). The zircon saturation in silicate melt yields crystallization temperature (Tzr) ~650 to 800°C for the Eastern Bastar Craton rocks. The P-T pseudosection modeling implies EBC granites which are crystallized at 700-750°C, at 0.4 to 0.6 GPa. The SHRIMP U-Pb ages from magmatic zircon yield an upper intercept at ~2470 Ma and a lower intercept at ~2100 Ma. When combined with the results of P-T pseudosection modeling, the geochemical and geochronological data classifies the Eastern Bastar Craton rocks as A2 granites that were emplaced during the amalgamation of Archean blocks leading to extended Ur formation. The ~2100 Ma age is correlated with mafic dyke emplacement and the Bastar Craton–Yilgarn Craton block disintegration before Paleoproterozoic Columbia supercontinent assembly.
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