Petrogenesis and tectonic implications of the Late Cretaceous to Paleogene calc-alkaline volcanic rocks, Ladakh Himalaya

Abstract

One of the most widespread volcanic suites exposed in the northwest Himalaya is the Khardung volcanic suite sandwiched between the Ladakh Batholith in the south and the Karakoram Batholith in the north. These volcanic rocks show a transition from andesite, dacite to more evolved rhyolite and have a calc-alkaline affinity. They display large ion lithophile elements (Rb, Sr, Ba, U, Pb) enrichment and depletion of high field strength elements (Nb, Ta, Hf, Ti) with increasing Eu negative anomaly from andesite to rhyolite. Bulk-rock Liquid Line of Descent (LLD) modelling shows that fractional crystallization played a dominant role in their petrogenesis. The calculated zircon saturation temperature (TZr) in andesitic magma (745 °C) is higher than the dacitic and rhyolitic magmas (682 °C). Andesites have zircon ages of 69–68 Ma, whereas more evolved dacite and rhyolite yield younger ages (59–64 Ma) that are consistent with their generation in the last stage of magmatism in an active continental marginal setting. Geochemical and geochronological findings of this study demonstrate that Khardung volcanic rocks were derived through two major magmatic events. These events occurred during the Late Cretaceous to the Paleocene Epoch due to the subduction of the Neo-Tethyan oceanic slab underneath the Eurasian plate boundary before the main collision between India and Eurasia.