U–Pb (zircon) geochronologic constraint on tectono-magmatic evolution of Chaur granitoid complex (CGC) of Himachal Himalaya, NW India: implications for the Neoproterozoic magmatism related to Grenvillian orogeny and assembly of the Rodinia supercontinent

Abstract

Many elongated, lenticular intrusive granitoids of various ages are scattered within the Lesser Himalayan metamorphic belt, all along the ~ 2500 km length of the Himalaya. The Neoproterozoic Chaur granitoid complex (CGC) of Chaur area is characterized by foliated and non-foliated peraluminous granites occurring as an isolated granitoid body within the Jutogh group. In this work, we present the whole-rock geochemical data of six samples and U–Pb (zircon) geochronology of two different granites of the CGC and one granitic gneiss sample of Jutogh group from Himachal Pradesh of NW Himalaya. Our newly obtained results of U–Pb (zircon) geochronological age populations from all granitoid sample yield age between 766 and 1080 Ma with few younger phases and older inherited ages. We obtained U–Pb (zircon) ages from two sample of the CGC, out of which one gives the two prominent age spectra for 206Pb/238U with weighted mean age of 826 ± 4.97/9.74 Ma, MSWD = 0.65, n = 8) and 868 ± 6.21/12.17 Ma, MSWD = 1.28, n = 7). Similarly, another granite of CGC gives the weight mean age of 929 ± 6.48/12.70 Ma (MSWD = 1.28, n = 11). The granitic gneiss of the Jutogh group also gives two prominent age spectra for 206Pb/238U, with weighted mean age of 861 ± 8.27/16.21 Ma (MSWD = 0.31, n = 10) and 932 ± 10.0/19.6 Ma (MSWD = 1.57, n = 8). The whole-rock geochemical data show calc-alkaline composition of all six samples and suggest a subduction-related accretion setup. The depletion in the Nb, Sr, P and Ti in CGC indicates a magmatic arc type magma. U–Pb (zircon) ages of all three samples have a similar phase of crystallization and we defined as ~ 930 Ma age of crystallization of CGC. The whole-rock geochemical data suggest that all the three samples possibly came from the same magma source during the Neoproterozoic magmatic events in the northern marginal part of the Indian plate. It is envisaged that the unknown microcontinents present in the northern margin collide with the Indian plate and the subduction process coincides with the onset of the Grenvillian orogeny during the Neoproterozoic. The extension of these minor collision orogen may have been connected with Lhasa, Trim as well as Greater India blocks. In this collisional process, the crustal melt was generated and intruded in the form of CGC within the pre-existing Paleoproterozoic crust of Indian plate. The whole process indicates that the subduction of unknown microcontinent under the Indian plate may be correlated with the Grenvillian orogeny and formation of the Rodinia supercontinent during Neoproterozoic.