U-Pb zircon ages and Sm-Nd isotopic characteristics of the Lesser and Great Himalayan sequences, Uttarakhand Himalaya, and their regional tectonic implications

Abstract

Detrital zircons (DZ) and Nd isotopic characteristics constraint maximum depositional ages of two distinct Paleoproterozoic and Neoproterozoic terranes across the Main Central Thrust zone (Munsiari Group) in the Himalaya. New DZ ages and Nd isotopic characters are reported from the Inner Lesser Himalaya (iLH) sedimentary belt (Berinag Group quartzite) and the Munsiari Group through the Great Himalayan Sequence (GHS–Vaikrita Group) across the MCT to the lower parts of the Tethyan Himalayan Sequence (THS) along the Alaknanda–Dhauli Ganga valleys, Uttarakhand Himalaya. The iLH Berinag Group quartzite yielded nearly unimodal DZ U-Pb ages between 2.05 and 1.80 Ga with εNd(0) values of −17 and −23, while the overthrust Munsiari Group, bounded by the Munsiari Thrust at the base and the Vaikrita Thrust (MCT) at the top, represents the Proterozoic magmatic arc with ∼1.95 and 1.89 Ga U-Pb zircon age population with an average of −25 εNd(0) value; the arc developed during the Columbia Supercontinent assembly. In contrast, overthrust Great Himalayan Sequence (GHS–Vaikrita Group) above the MCT is characterized by entirely new Neoproterozoic 1.05–0.85 Ga zircon population, which appears for the first time in this sequence, and has higher εNd(0) values (average −16). Tectonically overlying the GHS, the Tethyan Himalayan Sequence (THS) has first appearance of the Early Paleozoic detrital zircons, with its εNd(0) values like the GHS. Broadly, these characters persist throughout the Himalayan belt from Himachal to NE Himalaya. The iLH sediments were possibly derived from northernly ∼1.9 Ga magmatic arc, and southern the Archean–Proterozoic Aravalli–Bundelkhand nuclei of the Indian craton. Potential sources for the GHS sediments may be a northerly ‘destroyed’ Neoproterozoic magmatic arc whose remnants exists within the Himalaya as the Neoproterozoic granitoids, and possibly be the iLH sedimentary belt, an ‘In-board’ Aravalli–Delhi Fold Belt (ADFB)–Central Indian Tectonic Zone (CITZ) in the south.