Paleoproterozoic to Cambro-Ordovician crustal evolution in the northern Indian margin

Abstract

The northern margin of the Indian continental plate had undergone multiple tectonic events associated with the supercontinent assemblies and breakups before the Cenozoic collision of the Indian and Eurasian plates. Whole-rock geochemical, zircon U–Pb geochronology, Lu–Hf and O isotopic study of the granites and granite gneisses exposed in the west Kameng and Subansiri regions of Arunachal Himalaya has been carried out to understand the crustal evolution of the northern Indian margin during the Paleoproterozoic to Cambro-Ordovician. Bomdila granite gneisses of the west Kameng yielded zircon U–Pb ages of 1827 ± 24 Ma and 1753 ± 8 Ma, with εHf values ranging from –7.3 to +1.0 and δ18O values of 6.38–10.44 ‰, indicating a heterogeneous source derived from recycled crust and juvenile components with a significant incorporation of sediments. Geochemical signatures indicate a continental arc setting during the Columbia assembly. Tonian magmatism in the Dirang area (879–799 Ma) and the Ziro Valley (886 ± 13 Ma) of Subansiri area represent the eastern Himalayan vestiges of the Tonian crust associated with the Rodinia assembly. Bomdila granite yielded a younger emplacement age of 517 ± 4 Ma with εHf values between –9.3 to +0.4, indicating mixed sources with dominant recycled crustal and minor juvenile components. Ziro granite (509 ± 26 Ma) and Potin granite gneiss (520 ± 3 Ma) of Subansiri area yielded subchondritic εHf values of –9.6 to –6.6 and –16.8 to –3.6 respectively, indicating a recycled crustal-derived heterogeneous source. The zircons of the Bomdila granite, Ziro granite, and Potin granite gneiss show similar ranges of δ18O values: 6.34–8.78 ‰, 6.60–9.14 ‰ and 6.63–9.80 ‰ respectively, suggesting a moderate to high incorporation of sediments in the generation of these rocks during the widespread Cambro-Ordovician magmatism in the northern margin of India. Show more