CENOZOIC PALEOELEVATION HISTORY OF THE LUNPOLA BASIN IN CENTRAL TIBET: NEW EVIDENCE FROM VOLCANIC GLASS HYDROGEN ISOTOPES AND A CRITICAL REVIEW

The paleoelevation history and geodynamic evolution of the Bangong suture zone in the central Tibetan Plateau are hotly debated, with existing estimates showing contrasting results. Acknowledging the complexity of hydrologic processes in continental interiors, we first demonstrate that stable isotope-based paleoaltimetry, with necessary adjustment to account for moisture mixing, is applicable in Central Tibet. We use this understanding to further explore the paleoelevation of the Lunpola Basin along the Bangong suture. Tuff zircon U-Pb ages between 14 and 21 Ma provide new constraints on the early–middle Miocene Dingqinghu Formation. Volcanic glass hydrogen isotopes of these tuff samples yield dD values between -34‰ to -124‰. Through the integration of the new hydrogen isotope data with previously published oxygen isotope data of carbonate from the same Dingqinghu Formation lacustrine strata (21–20 Ma), we derive the stable isotopes of paleo-precipitation by reconstructing the local meteoric water evaporation line to provide improved paleoelevation estimates. The new calculations indicate that the precipitation-weighted mean elevation of the Lunpola Basin catchment was likely at 4.2–4.9 km during the early Miocene. We use these results and a review of existing paleoelevation studies to propose a three-stage topographic growth model for Central Tibet. The paleoelevation history highlights the significant contribution of convective removal of the lower lithosphere, underthrusting of the Indian lower crust, and middle–lower crustal flow to the surface uplift in Central Tibet.