Palaeoproterozoic S‐type granites from Garhwal Himalaya, NW India: Geochemistry, Sm–Nd isotope systematics and tectonic implications

Abstract

A combined geochemical and Sm–Nd isotopic study on the Palaeoproterozoic (1,845 Ma) granites of the Lesser Himalayan Crystalline Sequence (LHCS) in the Garhwal region of NW India has been done in the present study. These granite samples are characterized by high silica, alumina, and potash and belong to a peraluminous to strongly peraluminous series, having molar A/CNK values of 1.01 to 2.4. The low P2O5 contents and its negative correlation with SiO2 presiding out that the granites have S‐type affinity, also supported by various classification diagrams (ACF; SiO2 vs. P2O5, Na2O + K2O‐CaO, and Th). The concentration of trace elements Ba, Sr, Nb, and Ti are low, and Rb, Th, U, and Pb are found to be high. The granites have low total rare earth elements contents of 56.19–229.16 ppm with enrichment in Light rare earth elements (LREE) ([La/Yb]N = 1.61–15.08) and negative europium anomaly (Eu/Eu* = 0.12–0.31). Sm–Nd isotope studies were also performed for three granite samples. Estimated model ages as 2.5–2.7 Ga, indicates the contribution of the Archean crustal substrate as their protolith source. Therefore, we assume that the melting of metasedimentary rocks with Archean protolith can form these peraluminous granites in an accretional–collisional event, during the Palaeoproterozoic on the western flank of the Columbia supercontinent.