ΔD VALUES OF SHEAR ZONE MICAS FROM LHAGOI KANGRI IN SOUTH-CENTRAL TIBET SUGGEST A HIGH HIMALAYA BY THE MID-MIOCENE

The uplift history of the Himalaya and Tibet is crucial to understanding both the kinematic evolution of the orogen and past Asian climate patterns. However, the timing and spatial variation of the growth of this orogenic system remains poorly constrained. Here we provide estimates of the δD value of paleoprecipitation from mylonitic micas in the Lhagoi Kangri range in southern Tibet, which previous work suggests date to ~16 Ma. Stable isotope analyses of mica formed in the shear zone yield very low δD values, similar to those recorded around Mt. Everest ~120 km to the southwest. Assuming temperatures of equilibration of 550°C, these mica δD values indicate very low δD values for meteoric water that interacted with the mica at depth along the footwall of the shear zone. The reconstructed δD values for meteoric water suggest that the Lhagoi Kangri area attained high elevation by the time of shear zone displacement at ~16 Ma. This is consistent with similar studies conducted near Mt. Everest that show that the Himalaya had attained near-modern elevations by the early Miocene.