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• Hydrothermal helium is mainly from radiogenic production in the crust with 7.52 % is mantle derived. • CO 2 is mainly constrained by both decarbonization of Tethyan marine carbonate rocks and mantle fluid. • The He-CO 2 system is constrained by the regional magmatic intrusions and degassing process. • The contrasting slab subduction style and the south boundary of EHS are constrained by helium isotopes. • Location of mantle suture in EHS is extended and the south boundary is also constrained by helium isotopes. While understanding the origins of volatiles has strong implications on heat and tectonic processes, the relationship has not well understood, especially in the Eastern Himalayan Syntaxis (EHS) in the Tibetan Plateau, where tectonic framework, petrologic properties, stress field, and geomorphic water system changes greatly due to the strongest continental collision. Based on samples from warm/hot springs in the EHS, geothermal fluid is sourced from local precipitation and simultaneously recharged by deeply-sourced mantle volatiles. Volatiles from hydrothermal systems are mixture of crustal and mantle origin, in which helium is mainly from radiogenic production in the crust with only up to 7.52% is mantle derived whereas CO 2 is mainly constrained by both decarbonization of Tethyan marine carbonate rocks and mantle volatiles. The helium fluxes are estimated to be almost 1–2 orders higher than some representative volcanically and tectonically active continental regions. The He-CO 2 system is dominantly constrained by the regional magmatic intrusions and hydrothermal degassing process. The boundary of the Indian plate underplating beneath Tibet is extended eastward to across the EHS by evidences from He isotope and this boundary is probably the south boundary of the EHS. Differences of helium isotopes between the EHS and its southeastern region indicate the contrasting slab subduction style in the deep structure. These results present some quantitative constraints for the interpretations of regional tectonic processes on transportation of deeply-sourced volatiles and its indications on continental collision style and present essential basis for understanding volatiles degassing and cycling in the continental collision settings. [ABSTRACT FROM AUTHOR]

Important fault zone processes can be discerned from the hydrothermal fluid circulation associated with active seismic sources. This study focused on the geochemical and isotopic features of the thermal waters along the Ganzi-Yushu fault (GZYSF) located in the eastern Tibetan Plateau. 22 spring samples were collected to characterize the chemical compositions and calculate the geothermal reservoir temperatures. The hydrothermal waters are mainly recharged by meteoric water based on the δ18O and δ2H values. Immature waters with a Na + -HCO 3 - or Ca2+(Mg2+)-HCO 3 - composition were recognized in the study area, combined with the poor correlation between K+, Na+, Mg2+, HCO 3 − and Cl− suggesting a shallow hydrothermal fluid source. The 87Sr/86Sr ratios and high concentrations of B (from 20.3 to 9445 μg/L) and Li (from 3.04 to 2380 μg/L) show a dissolution of silicate minerals containing calcium and magnesium during fluid circulation. The geothermometry in the silicon-enthalpy system suggested equilibrium temperatures up to 146 °C, whereas most are low temperatures. The shallow geothermal fields along GZYSF show that most large earthquakes (M＞5) were distributed in the transitional zone between high-value area and low-value area of the shallow geothermal field, suggesting a potential genetic link between geothermal field structure and earthquake nucleation along active faults. In conclusion, we proposed a conceptual model to portray the fluid circulation process. Such work can provide insights into the potential geothermal resource in Tibetan Plateau, and also investigate the processes controlling the fluid chemistry and the correlation with occurrence of earthquakes in the region. • Characterize the chemical compositions, analyze the isotopic features and calculate the geothermal reservoir temperatures. • Most earthquakes (M > 5) were distributed in the transitional zone of the shallow geothermal field. • Put forward a genetic link between geothermal field structure and earthquake nucleation along active faults. • Provide insights into the potential geothermal resource in Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• As, Cr, B and F were the trace elements with high concentrations in the Gulu-Yadong rift. • Water quality throughout the whole rift are heterogeneous. • Subduction-related magmatic processes, leaching and water-rock interaction are the controlling factors of trace elements in the thermal water. • Trace elements in geothermal water is a non-negligible environmental and health issue in the Tibetan Plateau. Thermal springs are enriched in many trace elements that are closely related to environmental and human health. The occurrence of trace elements in groundwater systems is one of the most significant environmental and public health concerns. The northward subduction of the Indian continental lithosphere beneath the Asian continent has produced an ongoing continental subduction zone. The Tibetan Plateau serves as the 'Water Tower of Asia', supplying drinking water to more than one billion residents in Asia. In this study, eighteen geothermal springs in the Gulu-Yadong Rrift (GYR) were selected for investigation of the geochemical characteristics of their trace elements. The geological process–related geochemical characteristics of trace elements in geothermal springs in the GYR were quantitatively assessed. The results indicated that there were high concentrations of Cr, As, B, and F in the geothermal waters in the GYR. The concentrations of Cr, As and B greatly exceeded the World Health Organization (WHO) guidelines for drinking water. The water quality throughout the whole rift was spatially heterogeneous. The concentrations of trace elements in only six geothermal springs were within the guidelines of the WHO, while the concentrations of trace elements in eleven geothermal springs considerably exceeded the WHO guidelines. Continental subduction–related magmatic processes, leaching and water-rock interactions may be the main factors controlling trace elements in the geothermal water. The deep circulation of the thermal water facilitated the addition of upwelling hot materials and magmatic fluids into the shallow aquifers, as well as enhancing the water-rock interactions. The results of this study indicate that geological processes have a large influence on the geochemical characteristics of trace elements in geothermal springs in the Tibetan Plateau. It is a non-negligible environmental and health issue in the plateau. [ABSTRACT FROM AUTHOR]

The southeast Tibetan Plateau is a region with high level seismic activity and strong hydrothermal activity. Several large (7.5 > M > 7) historical earthquakes have occurred in the Litang fault zone (LFZ), eastern Tibetan Plateau since 1700. Litang Ms 5.1 earthquake occurred On Sept 23, 2016, indicating the reactivation of the LFZ. This study was undertaken to elucidate spatial-temporal variations of the hot spring gas geochemistry along the LFZ from Jun 2010 to April 2016. The chemical components, He, Ne and C isotropic ratios of bubbling gas samples taken from 18 hot springs along LFZ were investigated. Helium isotope ratios ( 3 He/ 4 He) measured in hot springs varied from 0.06 to 0.93 Ra (Ra = air 3 He/ 4 He = 1.39 × 10 −6 ), with mantle-derivd He up to 11.1% in the LFZ (assuming R/Ra = 8 for mantle) indicated the fault was a crustal-scale feature that acts as a conduit for deep fluid from the mantle. CO 2 concentrations of the majority of hot spring gas samples were ≥80 vol%, CO 2 / 3 He ratios varied from 1.4 to 929.5 × 10 10 , and δ 13 C CO2 values varied from −19.2‰ to −2.3‰ (vs. PDB). The proportions of mantle-derived CO 2 varied from 0 to 1.8%. Crustal marine limestone was the major contributor (>75%) to the carbon inventory of the majority of hot spring gas samples. Before Litang Ms 5.1 earthquake, the 3 He/ 4 He ratios obviously increased in the Heni spring from May 2013 to Apr 2016. The geographical distribution of the mantle-derivd He decreased from east to west along 30°N in the southeast Tibetan Plateau relative to a corresponding increase in the radiogenic component. The gas geochemical data suggested that the upwelling mantle fluids into the crust play an important role in seismic activity in the strike-slip faults along 30°N in the southeast Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• The geothermal waters of in the LXF zone are contaminated by Na-Cl type fluid obviously. • The lower crust flows through the LXF from west to east, causes internal deformation of the LXF zone and occur earthquakes. • Monitoring a proper geothermal waters and gases will help us to study the pre-seismic hydrochemical precursors. Geothermal fluid is considered to be one of the important methods of earthquake forecasting, and some achievements have been made in previous studies. However, there is still a lot of work to be done before geothermal fluid can actually be used for earthquake forecasting. Lijiang-Xiaojinhe fault (LXF) which is a quake-prone region that lies on the border of Tibetan Plateau and Yangtze block is a good natural experimental field for earthquake research. In this contribution, we performed a systematic hydrogeochemistry and isotopic analysis of the geothermal waters and gases in the LXF zone. High Cl- (0.69–529.44 mg/L) concentrations in hot springs indicate that they are contaminated by deep fluid obviously. Further continuous observation (2020–2022) indicates that there are at least four times correspondence between ion concentration in two hot springs (Jinhe (94) and Xiaoshuiping (331)). Two earthquakes (M L 5.2 earthquake on January 02, 2022 and M L 4.6 earthquake on April 16, 2022) in Ninglang are only 50 km away from 331 hot spring, and obvious abnormal concentrations of Cl-, Na+ and SO 4 2- were observed before the earthquakes. Combined with geological background and previous studies, we propose that lower crustal flow could be the reason why earthquake-prone in LXF. The lower crust flow through the LXF from northwest to southeast, causes internal deformation of the LXF zone. Then, a large amount of groundwater infiltrates deep underground along the fault, strengthens the pore fluid pressure, promotes the water–rock reaction, weakens fault zone, and trigger earthquakes. Ion concentrations in hot springs are sensitive to seismic activity in LXF. Unusually high or low ion concentrations in hot springs could represent the process of earthquake development, monitoring proper geothermal waters and gases in LXF will help us to study the pre-seismic hydrochemical precursors, and have a potential to provide important bases for earthquake forecasting. [ABSTRACT FROM AUTHOR]

• The volatiles of the hot springs come mainly from the crust, with only a small amount from the mantle. • The tectonic stress field at the converging plate boundary limits the crustal helium flux. • Carbon sequestration of calcite precipitates slows down carbon flux in the collision zone. • Crust within the convergent boundary has the potential to produce a significant proportion of volatiles. • Coupled overpressure and stress fields in the rigid crust may lead to high seismic risk in this area. The spatial and temporal evolutionary mechanisms of volatile components at plate boundaries and their potential as earthquake precursors are not well understood. Based on observations of He–CO 2 from 19 hot-spring gases in the Lancang River fault zone, Yunnan Province, the results show that the volatiles mainly come from the crust. The combined He isotope, He–CO 2 relationships, and δ13C–CO 2 values of the hot-spring volatiles indicate that it is a mixture of mantle and crustal fluids. These are related to the radiogenic He production caused by crustal U and Th elements with <5% mantle-derived He, whereas C is mainly from the metamorphic decarbonization of Tethyan marine carbonate rocks. Based on the He–CO 2 isotopic relationship, crustal volatiles flux with a significant proportion were determined within a non-volcanic area, which was estimated to be 9–132 mol a−1, and CO 2 degassing was estimated to be 2–120 × 109 mol a−1. These results are comparable to those of some volcanic areas and large seismically-active fault zones (such as the San Andreas Fault zone). The compressional stress field of the rigid crust near the study area leads to the low permeability of large faults and CO 2 degassing from the hydrothermal system, resulting in chemical precipitation that further blocks the shallow crust conduits and deduced overpressure below the hydrothermal reservoir, which may be the cause of the presence of earthquakes with magnitudes greater than 7 in the Lancang River fault zone. The results are significant for elements cycling of converging plate boundaries and earthquake hazards monitoring. [ABSTRACT FROM AUTHOR]

The outpouring hot spring water is deep circulated groundwater and its chemical constituents act as information carriers of the hydrological setting, including the recharge source, circulation path, and reservoir properties. However, the temporal variation in hydrochemical components and their inducing mechanisms remain to be elucidated. In this study, hot springs along the Anninghe-Zemuhe Fault, a controlling fault on the eastern edge of the Tibetan Plateau, were investigated. According to the spatial chemical variations of the sixteen hot springs and the two-year hydrochemical monitoring results of four hot springs, the aquifers in such fault-controlled regions exhibit heterogeneous anisotropy and elastic properties. Earthquake activities were found to play a significant role in both spatial and temporal changes in chemical compositions. We found that the waters with the highest reservoir temperatures (∼100 °C) and deepest circulation depth (∼3 km) outcropped in the north of the fault, where earthquakes occur more intensively, deeply, and stronger than those in other parts of the fault. During the stress accumulating and releasing processes in the earthquake sequence, the fractured aquifer systems are elastic and subject to impulsive mixing with subordinate fracture waters which induced hydrochemical changes at different levels. The chemical constituents responded to seismic energy densities as low as 6.5 × 10−4 J/m3, showing superiority over the groundwater monitoring wells. However, earthquakes that occurred in a tectonically independent area or with an inappropriate stress loading-unloading direction could fail to trigger a distinguishable mixing process with apparent chemical fluctuations. These findings provide insights into the hydrochemical response to earthquakes in orogenic areas and further draw attention to hydrochemical changes in hot spring waters in seismic studies. • Hot spring waters circulate deeply where earthquakes occurred intensively. • Fractured aquifers in orogenic regions are elastic, heterogeneous, and anisotropic. • 3D analysis of the temporal chemical change uncovers the impulsive mixing process. • Mixing with subordinate fracture waters is triggered during the earthquake cycle. [ABSTRACT FROM AUTHOR]

The lithospheric structure of the Tibetan Plateau plays a key role in explaining the underlying plateau formation mechanism(s) and growth history. Although many studies have focused on the Moho discontinuity, lithosphere boundary, and lithospheric structure of central and eastern Tibet, there are few corresponding constraints for western Tibet. In this contribution, we systematically investigated the lithosphere in western Tibet by analyzing the He and C isotopes of seven hydrothermal spring systems along the southeastern segment of the Karakorum fault. We found a high Rc/Ra ratio (1.298) for springs along the Karakorum fault, suggesting that the fault plays a key role as a lithospheric-scale conduit for fluid uplift after mantle degassing. In addition, we identified two different origins of the gases at thermal springs, which may reflect two distinct mantle sources. We infer that the locations of these springs reflect the boundary between the Indian and Asian mantles, which is consistent with the geophysics-based interpretations of a "mantle suture" along the Karakorum fault. Our work confirms the boundary between the Indian and Asian mantle, which provides geochemical support to the model of the subduction of Indian lithosphere. [ABSTRACT FROM AUTHOR]

Geofluids from natural springs connect with the crust and/or mantle in many cases, and their geochemical anomalies could be significant for the study on faults activity and even earthquakes. Several natural springs are distributed along the Lenglongling fault zone (LLLFZ) in the northeastern margin of the Tibetan Plateau, where the M s 6.9 Menyuan earthquake occurred on January 8th, 2022. Based on chemical and isotopic compositions (δD, δ18O, δ13C, and 3He/4He) of water and gas samples, the origin of geofluids and their potential correlation with fault activity even including earthquakes are preliminarily assessed in this paper. The δ13C CO2 values and 3He/4He ratios showed that the gas originating from the crust was associated with the metamorphism of carbonate rocks, whereas the δ18O and δD values of water samples indicated that the natural springs were predominantly infiltrated with precipitations from local mountains ranging 3.7 - 5.5 km in height. Obvious changes of Ca2+ and HCO 3 − concentrations in SZK spring waters in the surface rupture zones were observed in a short period (about three months) after the main shock, in contrast to those of the GSK springs far from the surface rupture zones. Such variations might be correlated with the stress increase prior to the 2022 Menyuan M s 6.9 earthquake. The mechanical fracturing of surrounding limestone rocks during the slipping movement of LLLF could facilitate the water-rock interactions. Compared to three-month observations after the main shock, relatively higher concentrations of HCO 3 − and heavier δ18O H 2 O values of the LHG springs were also observed in the short-term period. The shallow stored formation water might be squeezed along the cracks and rose to the surface during earthquake tremors, causing a sandblasting water phenomenon. • Ionic concentration of spring water showed anomalies with Menyuan M S 6.9 earthquake. • Two distinct causes of hydro-chemical anomalies revealed. • Bubbling CO 2 originated mainly from metamorphic and weathering carbonate in the crust. [ABSTRACT FROM AUTHOR]

• We report chemical compositions and He-C isotope data for hydrothermal gases. • He and CO 2 degassing is quantitatively constrained for a Y-shaped fault system. • Slip rates positively correlate with 3He/4He of fluids in a hydrodynamic model. • Deep fluids may contribute to overpressure involved in seismogenic processes. Degassing of deeply-derived fluids (e.g., He and CO 2) prevails along seismically active faults in continental collision settings such as the Tibetan Plateau, where potential insights into seismogenesis through tectonic degassing remain less understood. Here, we present a quantitative geochemical study on hydrothermal gases from a Y-shaped active fault system in the eastern Tibetan Plateau, aiming to delineate how tectonic degassing (e.g., fluid origin and transport) may be linked to seismogenic processes in continental collision settings. Our results show that (i) vigorous degassing of mantle- and crustal-derived CO 2 -rich fluids (3He/4He = 0.94–2.73 Ra, where Ra = air 3He/4He; δ13C CO2 = −8.9 to −2.6‰) dominates the axis zone of the Y-shaped active fault system, while (ii) crustal fluid inputs become more prevalent along its NW branching fault (3He/4He = 0.03–0.62 Ra; δ13C CO2 = −8.9 to −0.2‰) and the NE and SE branches (3He/4He = 0.01–0.07 Ra; δ13C CO2 = −17.3 to −5.2‰). Localized mantle melting and metamorphic decarbonization likely produce the CO 2 -rich fluids, which could account for significantly higher CO 2 flux in the axis zone (9.66 × 109 mol/yr) than along the NW branch (1.25 × 109 mol/yr). The well-correlated 3He/4He ratios and slip rates suggest a genetic model in which the uprising CO 2 -rich fluids may facilitate rapid fault slip and enhanced fault permeability, which could in turn lead to efficient mantle He degassing. Taking the fluid origin and transport, CO 2 fluxes, and regional seismicity together, we suggest that the deeply-derived CO 2 -rich fluids may contribute to overpressure involved in seismogenic processes of the Y-shaped active fault system. [ABSTRACT FROM AUTHOR]