Correlation of Precambrian-Cambrian sedimentary successions across northern India and the utility of isotopic signatures of Himalayan lithotectonic zones

Abstract

A common view in Himalayan geology is that differences in detrital zircon age distributions and whole-rock neodymium isotopic compositions (εNd) distinguish lithotectonic zones within the system. Such differences are used to map these zones and to locate their modern boundaries, as well as to infer ancient terrane boundaries. We test the utility of this approach using integrated geochemical, geochronological, and sedimentological data from the Himalayan successions of northern India and relatively undeformed, age-equivalent successions of the Indian craton. U-Pb geochronology of detrital zircons from cratonic successions of the Vindhyan, Ganga, and Marwar supergroups and the "inner" and "outer" Lesser Himalaya lithotectonic zones show that rocks of similar depositional age bear strikingly similar detrital zircon age distributions throughout the entire region. A sharp change in εNd occurs within the "inner" Lesser Himalaya and correlates with a regional unconformity recognized on the craton, here constrained to span a period of ~. 500. million years. Results demonstrate that isotopic differences among the lithotectonic zones relate primarily to differences in the depositional ages of their constituent rocks, and that all parts of the Himalaya were in sediment-source continuity with the Indian craton from the late Paleoproterozoic to the early Cambrian. Isotopic "signatures" may vary as much within individual Himalayan lithotectonic zones as between such zones and no lithotectonic zone can be characterized by such data alone. © 2011.