δD VALUES OF SHEAR ZONE MICAS FROM THE LHAGOI KANGRI DOME SUGGEST HIGHER REGIONAL ELEVATION IN THE NORTHERN HIMALAYA DURING THE MID-MIOCENE

The uplift history of the Himalayan – Tibetan orogen is crucial to understanding the geodynamic evolution of the orogen and its influence on the Asian climate system. Here we reconstruct paleoelevation ~13 Ma in the northern Himalaya using the hydrogen isotope composition (δD) of synkinematic micas in mylonitic quartzite and paragneiss. These micas equilibrated at high temperatures (447 ± 48°C, determined by oxygen isotope fractionation of quartz-muscovite mineral pairs) with a water composition (δD_w = -179 ± 5‰ VSMOW) consistent with high elevation precipitation that infiltrated into the ductile shear zone bounding the Lhagoi Kangri dome. We used multiple lapse rates to compare this value with contemporaneous sea-level precipitation recorded in Siwalik paleosol carbonate. 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, close to 1 km higher than the modern catchment average elevation (~5 km). This result is similar to late Miocene paleoelevation data from the Zhada basin ~850 km along strike to the west and shows that more than one area of the northern Himalaya experienced elevation loss during the late Neogene.