The central-northern section of the Yadong-Gulu rift is one of the important geothermal activity areas in the Mediterranean-Himalayan geothermal belt.The deep circulation process of the geothermal system in the central-northern section of the Yadong-Gulu rift is very complex and still unclear,which has a significant impact on the evaluation of geothermal resources in this region.Attracting researcher's attention to the geological structure and geothermal system of this region.The deep seismic reflection profiles of the Himalaya and Tibetan Plateau confirm the existence of magmatic heat sources in the geothermal system in the middle and northern section of the Yadong-Gulu rift.The central-northern section of the Yadong-Gulu rift is enriched in Li,Rb,and Cs elements in geothermal fluid,which may be derived from deep magmatic hydrothermal fluid or from water-rock interaction during runoff process.Isotopic characteristics are important evidence of material sources and are an important method for clarifying the runoff process.We systematically sampled the geothermal water in the central and northern sections of the Yadong-Gulu fault zone and measured carbon,sulfur,and boron isotopes.Samples of geothermal water were collected and analyzed from typical hot fields and multiple geothermal display areas in the study area.The carbon sulfur and boron isotope analysis of geothermal fluids in the middle and northern section of Yadong-Gulu rift zone shows that the stable isotope characteristics are derived from the leaching of geothermal fluids to surrounding rock and formation and water-rock interaction.The main source of carbon in this geothermal system is the dissolution of carbonates,which is related to the distribution of carbonate strata in the region.The δ34S values of Gulu and Xumai geothermal fields have a large dispersion,indicating that the source of sulfur is not single.The δ34S isotopic values are within the range of atmospheric carbonate and evaporative carbonate,indicating that the source of sulfur is atmospheric precipitation and sulfate minerals in the thermal reservoir.The Gulu geothermal field has a low δ11B value and a low Cl/B ratio,high boron content,and relatively concentrated boron content and boron isotopic values,indicating that boron mainly originates from leaching operations of geothermal fluid on surrounding rocks.The boron content in atmospheric precipitation and snow melt water is extremely low,mainly playing a diluting role in boron content in geothermal water,without changing the δ11B value in geothermal water.The results of this study confirm that the underground thermal water in the northern segment of the Yadong-Gulu rift is mainly derived from atmospheric precipitation,with a small amount of magmatic fluid mixed in during deep circulation.
middle-northern section of Yadong-Gulu riftgeothermal fluidcarbon-sulfur-boron isotopehydrogeochemical processhydrothermal system
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