Effects of sustained tectonic uplift on groundwater systems in the Tibetan Plateau: Evidence from hydrochemistry and isotopes

The Tibetan Plateau has experienced sustained tectonic uplift that has inevitably led to changes in its groundwater system. Exploring the evolution of groundwater systems in geological history is an essential but difficult task, owing to the current lack of hydrogeological data. Hydrochemistry and isotope analysis guide interpreting the effects of tectonic uplift on groundwater systems. High-TDS (Total Dissolved Solids) groundwater and fresh groundwater exist adjacent to the same groundwater system in the Huangshui River Basin, which is a typical area affected by sustained uplift at the eastern foot of the Tibetan Plateau. The dating results for five terraces with Optically Stimulated Luminescence (OSL), Electron Spin Resonance (ESR), and 14 C indicated that the Huangshui River Basin has undergone at least five uplift events over the past 300000 years. Hydrochemical analysis revealed the presence of sulfate and carbonate dissolution in the high-TDS groundwater, which implies the effect of evaporation. However, hydrogen and oxygen isotopes indicate that the groundwater is minimally affected by modern evaporation. The sustained uplift of the Tibetan Plateau changed the groundwater system and transformed the former groundwater discharge areas into the present recharge areas. Evaporite minerals formed through continuous evaporation and concentration were located on T3 and higher terraces. The hydrochemical composition of these terraces is controlled by the dissolution of evaporite minerals, which are characterized by high TDS. These findings offer new insights into the evolution of groundwater flow systems and hydrogeochemical processes under sustained tectonic uplift and promote an understanding of hydrochemical evolution in tectonically active regions.