Chemical weathering of small watersheds in the upper reaches of Jinsha river on the eastern edge of the Qinghai–Tibet Plateau

•The main source of ions is controlled by the chemical weathering of carbonate rocks.•The total chemical weathering rate in the study area is at a low level.•Weak hydrothermal conditions slow down the chemical weathering process. Land chemical weathering is a crucial and common geological process on the Earth’s surface. Studying the surface chemical weathering process in basins is important to the net consumption rate of atmospheric CO2, climate change in geological history, and the global carbon cycle. In this study, a small watershed in the upper reaches of Jinsha River on the eastern edge of the Qinghai-Tibet Plateau is selected as the study area. By measuring the physical and chemical properties and the main ion content of the water in the watershed and by using the factor analysis method, the source of the main ion components in the water in the alpine basin and the characteristics of the chemical weathering of the basin rocks are examined. Results show that the pH value of surface water in the study area varies from 7.4 to 8.2, and the overall performance is moderately to weakly alkaline. The total salinity in the basin is between 52.42 and 398.19 mg/L, with an average value of 180.06 mg/L. The concentration of main cations in surface water follows the order Ca2+>Mg2+>Na+>K+. The concentration relationship of the main anions is in the order HCO3−>SO42−>Cl−, and the hydrochemical type is HCO3_Ca. The main source of ions in the study area is rock weathering, which is controlled by the chemical weathering of carbonate rocks. The contribution rates of carbonate (mainly dolomite and calcite dissolution), evaporite, and silicate to the dissolved matter in the river are 59.40%, 7.30%, and 3.00% respectively, and the contribution rate of CO2 in the atmosphere to the dissolved matter in the river is 30.30%. The total chemical weathering rate in the study area is 29.09 t/km2 ⋅a, which is at a low level, indicating that weak hydrothermal conditions slow down the chemical weathering process of rock minerals.