Cambro-Ordovician metamorphism from Lesser Himachal Himalaya and its implication in Gondwanaland assembly

Abstract

Abstract 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).