Maoya hot spring, as a famous earthquake monitoring site, is seldomly studied in terms of its genesis and deep geothermal process. In this paper, we investigated the chemical and isotopic composition of thermal water in Maoya and Maohuo in Litang to elucidate the hydrochemical characteristics and genesis of the geothermal waters.
The study results show that Maoya hot springs and Maohuo hot spring are of the Na-HCO₃ type as a result of dissolution processes involving feldspars from the reservoir rocks due to the water-CO₂-rock interaction during the deep circulation of the geothermal waters. According to the diagram of Cl^- and Na⁺ concentrations of the geothermal water samples, Cl^- in Maoya hot spring originates from the mixing of granodiorite and basalt aqueous solutions in the process of water rock interaction, while Cl^- in Maohuo hot spring mainly originates from granodiorite aqueous solutions. The stable isotope δD and δ¹⁸O composition of geothermal waters indicates that they are recharged by meteoric precipitation. The Maoya hot springs have the characteristics of higher concentration of ion components and slightly oxygen drifting compared with the Maohuo hot spring, indicating that they have a deeper circulation depth and experience a stronger water-rock interaction. In addition, the ratio of Cl^-that comes from deep source in Maoya hot springs is higher than that in Maohuo hot spring.
The high temperature geothermal water formed by deep circulation of meteoric water is mixed by the shallow cold water during the ascending process. We employed SiO₂ geothermometer and Si-enthalpy model to estimate the temperature of shallow reservoir after mixing with cold water and the temperature of deep reservoir and the mixing ratio of cold water, respectively. The results suggest that the temperature of shallow reservoir in Maoya thermal field is in the range of 75~103℃ and the temperature of deep reservoir in Maoya thermal field is about 235℃ and the mixing ratio of cold water ranges from 87% to 94%. Based on the temperature of deep reservoir, we calculated the depth of the geothermal cycle in Maoya area, which is close to 5km.
The heat source triggering the formation of this geothermal system mainly originates from mantle and partial melting body of the crust. In addition, Cenozoic granitoid magmatic residual heat and upper crust radioactive heat can also provide additional heat sources. During the process of surface cold water circulation from shallow to deep, on the one hand, it forms deep geothermal water through normal geothermal gradients, and on the other hand, the mantle fluid upwelling below the Litang Basin and partial melting in the middle crust further heat the groundwater to form a high-temperature deep reservoir. The deep geothermal water is transported to the surface along the Litang Fault under the effect of hydrostatic pressure and hydrothermal convection. During ascending process, the first mixing of groundwater with superficial cold water occurred due to the presence of structural cracks in the crust, and the temperature of the mixing water is about 100℃. When the geothermal water migrates to the near surface, it mixes with the pore water and bedrock fissure water in the basin for the second time, and the mixing proportion of cold water increases(about 90%). Finally, it emerges to the surface, forming a group of medium-low temperature hot springs.

Based on the analysis of fluid anomaly data and investigation of macro precursor of the M_S 8.0 Wenchuan earthquake,and having taken careful consideration of the difficulty and ability of predicting earthquake,we found that the failed prediction of the M_S 8.0 Wenchuan earthquake doesn't mean that earthquakes can't be predicted.There were,though not much in quantity,a certain amount of underground fluid anomalies and remarkable macro anomalies occurring before the earthquake.Though it is difficult to predict the earthquake basing on them,it is possible to be aware of the impending earthquake.To improve the ability of earthquake prediction,the paper proposes to innovate the present work and administrative systems,in which,earthquake monitoring,prediction and research are separate each other,and professional and local forces are separate each other,to change the present work state of computer-replacing-human brain and the work mode of the too early use of formality and standardization,and to attach greater importance to investigation and confirmation of precursory anomalies and to monitoring and studying macro anomalies.