Pre-Himalayan crustal evolution in the northern margin of India: Implications from zircon U–Pb, Hf and O isotope study of Chhota Shigri granitoids, Himachal Himalaya, Northwest India

Abstract

A systematic geochemical, geochronological (U−Pb), and isotopic study (Lu−Hf and O) of zircons from the northern margin of India has been carried out to understand the pre-Himalayan crustal evolution along the area. The rocks were characterized as granitoid and yielded two significant age peaks: 1018–715 Ma and 516–476 Ma, with sparse inherited cores of Paleoproterozoic to Archean ages, defining two major magmatic events (Tonian and Cambro-Ordovician) in the NW Himalaya. While Tonian ages are preserved in the zircon cores, the rims and numerous whole grains record the younger Cambro-Ordovician event. The Tonian zircon cores display εHf values ranging from –5.9 to +8.3, indicating both juvenile mantle-derived and recycled crustal sources. The Tonian zircon cores yield single-stage Hf model (T_DM) ages of 1.66–1.19 Ga and δ¹⁸O values of 5.75–10.88‰, suggesting that Tonian granitoids formed from mixed sources comprising juvenile material, recycled ancient crust and δ¹⁸O-rich supracrustal components. The Cambro-Ordovician zircons yielded εHf values from –27.4 to –4.0 and single-stage Hf model (T_DM) ages of 2.16–1.21 Ga, demonstrating extensive reworking of both Neoproterozoic crust and ancient crust occurred during the Cambro-Ordovician magmatism. Their elevated δ¹⁸O values (8.05–11.35‰) further support widespread crustal remelting with substantial incorporation of δ¹⁸O-rich supracrustal materials. These evidence the preservation of supercontinent (Rodinia) components within the NW Himalaya.