Was the Himalaya Higher During the Mid-Miocene?

Abstract

The uplift history of the Himalaya and Tibet is crucial to understanding both the geodynamic evolution of the orogen and its influence on the Asian climate system. Here we reconstruct paleoelevation in the northern Himalaya using the hydrogen isotope composition (δD) of synkinematic micas (dated to 13.4 ± 0.3 Ma) in a ductile shear zone bounding the Lhagoi Kangri dome. These micas equilibrated at high temperatures (447 ± 48°C) with a water composition (δD = -179‰ VSMOW) consistent with infiltration of high-elevation precipitation into the shear zone. We used multiple lapse rates to compare this value with contemporaneous sea-level precipitation recorded in Siwalik paleosol carbonate within the Himalayan foreland basin. These lapse rates provide paleoelevation estimates ranging from 5.8 – 6.5 km for the regional catchment that provided water to the shear zone during displacement, ~1 km higher than modern average elevation (~5 km). Similar late Miocene paleoelevation results from the Zhada basin ~850 km along strike to the west suggests that more than one area of the northern Himalaya experienced elevation loss during the late Neogene.