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• Classification of complex geothermal systems in the Gonghe Basin. • Geothermal gas and isotope characteristics of the Gonghe Basin. • Deep heat source indication based on fluid geochemistry. The Gonghe Basin is located in the northeast of the Tibetan Plateau and is rich in geothermal resources. In recent years, Hot Dry Rocks have been discovered in the basin, and related studies have suggested that localized melts in the middle and lower crust provide an additional heat source. However, there needs to be more conclusive evidence. In this paper, geothermal water chemistry and gas isotope samples from the Gonghe Basin and its neighboring areas were systematically collected. Comprehensive fluid geochemical analysis was carried out in conjunction with the distribution and nature of the regional fracture to propose the circulation pattern of the complex geothermal system and the source of the gas components in the Gonghe Basin. The results show that the hot water in the Gonghe Basin and its surroundings is recharged by meteoric water and can be classified into three types according to its hydrochemical and isotopic characteristics: deep-fluid type (deeper circulation depth or deeper burial of the geothermal reservoirs), runoff type (shallower circulation depth), and mixed type (shallow layered geothermal reservoirs at the center of the basin), with a gradual decrease in the temperature of the geothermal reservoirs accordingly. N 2 of atmospheric origin dominates the hot water gas. Except for the relatively high CO 2 concentration (7.44%) in the deep geothermal reservoir in the center of the basin, most of the samples contain low CO 2 concentration, which is mainly derived from decarbonization of carbonate rocks and sediments, and the contribution of mantle carbon release is almost zero; some of the hot water is detected with a slightly higher content of CH 4 , which is inferred to be of organic origin. The distribution of deep fractures provides a channel for the uplift of deep mantle-sourced volatiles, which makes some hot springs and geothermal wells show some mantle-sourced diagenesis of He, which provides some corroboration for the existence of partial melts in the crust. This understanding is significant for deepening the understanding of geothermal genesis in the northeast Tibetan Plateau and guiding future geothermal exploration in the region. [ABSTRACT FROM AUTHOR]

Abstract: Water level and chemistry of Lake Qinghai are sensitive to climate changes and are important for paleoclimatic implications. An accurate understanding of hydrological and chemical budgets is crucial for quantifying geochemical proxies and carbon cycle. Published results of water budget are firstly reviewed in this paper. Chemical budget and residence time of major dissolved constituents in the lake are estimated using reliable water budget and newly obtained data for seasonal water chemistry. The results indicate that carbonate weathering is the most important riverine process, resulting in dominance of Ca2+ and DIC for river waters and groundwater. Groundwater contribution to major dissolved constituents is relatively small (4.2 ± 0.5%). Wet atmospheric deposition contributes annually 7.4–44.0% soluble flux to the lake, resulting from eolian dust throughout the seasons. Estimates of chemical budget further suggest that (1) the Buha-type water dominates the chemical components of the lake water, (2) Na+, Cl−, Mg2+, and K+ in lake water are enriched owing to their conservative behaviors, and (3) precipitation of authigenic carbonates (low-Mg calcite, aragonite, and dolomite) transits quickly dissolved Ca2+ into the bottom sediments of the lake, resulting in very low Ca2+ in the lake water. Therefore, authigenic carbonates in the sediments hold potential information on the relative contribution of different solute inputs to the lake and the lake chemistry in the past. [Copyright &y& Elsevier]

Abstract: The Tibetan Plateau covers an area of about one fourth of Europe, has an average elevation over 4000m above sea level, and is the water sources for about 40% of world''s population. In order to foresee future changes in water quality, it is important to understand what pressures are governing the spatial variation in water chemistry. In this paper the chemistry including major ions and trace elements in the headwaters of four major Asian rivers (i.e. the Salween, Mekong, Yangtze River and Yarlung Tsangpo) in the Tibetan Plateau was studied. The results showed that the content of dissolved salts in these Tibetan rivers was relatively high compared to waters from other parts of the world. The chemical composition of the four rivers were rather similar, with Ca2+ and HCO3 − being the dominating ions. The exception was the Yangtze River on the Plateau, which was enriched in Na+, Cl−, SO4 2− and Li due to silicate weathering followed by strong evaporation caused by a negative water balance, dissolution of evaporites in the catchment and some drainage from saline lakes. The concentrations of heavy metals (Cu, Co, Cr, Ni, Cd, Pb, and Hg) and As, NH4 + were generally low in all the rivers. Anthropogenic impacts on the quality of the rivers were identified at a few locations in the Mekong River and Yarlung Tsangpo basins. Generally, the main spatial variation in chemical compositions of these under studied rivers was found to be governed mainly by difference in geological variation and regional climatic-environment. Climate change is, therefore, one of main determining factors on the water chemical characteristics of these headwaters of Asian major rivers in the Tibetan Plateau. [Copyright &y& Elsevier]