The Study Of Deep Source CO₂ Degasification And Carbon Cycle In The Southwest Of China

It is of significance to study the CO₂ degasification on the discordogenic fault. It is indispensable to calculating the earth's carbon content. It is also indispensable to making clear the geochemical circulation of carbon, the karst dynamic system of the carbon and the reasons of CO₂ content growth in atmosphere and recent intercurrent disasters. Besides, it is an important way of making clear deep characteristic of mantle and other geological processes.Samples of the typical hot springs of water, gas, tufa and rock were collected and analyzed systematically. Meanwhile, some items were examined both in the field and in the laboratory. Through the analyses of condition, the geologic background and the hydrochemistry and the isotope of the carbon and helium of the typical hot springs in the southwest of China, the general rules of the CO₂ degasification points in the southwest of china are explored and the CO₂ degasification is calculated on the whole.According to the results of water chemistry analysis of the typical hot springs in the southwest of China, combined with the nature of fault near hot springs and the characteristic of the earth conformation and small conformation, the condition of hot springs formation and the hydrogeochemistry characteristics are analyzed.The alkalinity of Tibet spring water is alkaline that is similar to that of other geothermal areas in the world. However, the spring water is acidic (pH<4) on the Tengchong plot in the west of Yunnan.The analysis of various kinds of geochemical indicator, for example B, Cs, Li, F and TDS, explains the close relation between the places of hot springs and the geologic structures. The results also indicate that the "fractional melting layers" of the depth crust exists in the backland of Qinghai-Tibet Plateau while volcanic magma chamber of Quaternary lies in the west of Yunnan. The converging spot of a great number of large and deep fault layers accompanied by intense metamorphism in the west of Sichuan decide the release of CO₂.The range of temperature of the hot springs is wide. The temperature reflects the degree of the active belt fault to a great extent. The temperature is in agreement with large and deep fault.The supply of the hot spring water mainly comes from atmospheric precipitation at the same time including water of the diagenesis or syngenesis.The Tengchong plot of the west of Yunnan is located on the India Plate and Eurasian Plate. The conformation activity and the geothermal activity are fierce. It has a great deal of CO₂ degasification points. The supply diversification of the hot springs to water on the Rehai geothermal area causes the major difference in water chemistry here. Some come from diagensis of magma and exogenous water. The isotope ratio of helium is high. Some come from mantle.Quaternary volcano is not found in the Gangdese and Himalayas of the Tibet. Strong hydrothermal activities exist in the plateau, especially from the middle to the south of the Tibet. The research shows the "fractional melting layers" in the depth of the crust is responsible for the hydrothermal activities. The analysis of the isotope ratio of helium proves the tiny amount of deep source substance.Due to their special geological structure, Nuding and Kangding etc. in the west of Sichuan plateau is called "Bermude of geology in China". There is not quaternary volcano. But because there is a junction of the Xianshui Rive fracture zone and Longmen Mountain fracture zone and meanwhile the fault cuts through the earth' crust here, the analysis of the Carbon and Helium isotope shows the existence of deep source substance. The hydrochemistry of the hot-spring water in the Kangding county and Luding county has abnormal area, such as B.Meanwhile the CO₂ degasification point releases various gases including N₂, CO₂, H₂S, CH₄, He, and so on. He gas is an inertia chemical element that cannot react with chemical action but physical process. So Helium and its isotope is a sensitive geochemistry tracer reagent that can distinguish the mantle-derived gases. There are different mother earth constitution will formative uneven distributing Helium isotopes. So the helium isotope shows mantle-derived on the west to this crust fault and less mantle-derived helium on the east. The distribution law of the helium isotope in space can also reflect the difference of the CO₂ degasification.The analysis of the "heat bump" show that it is probably the fractional melting layers which behave as low-velocity and high-conductivity lying in the geophysical exploration in the crust. The fractional melting layers are likely silicate fused mass, other than liquid with main component of water. The melting layers are not only providing heat energy for shallow hydrothermal system, but also supplying liquid and metallogenetic elements to them. The results of research suggest that the upper fractional melting layer has driven ampliate area's hydrothermal activities in the south Tibet, whereas the near surface upwelling makes melting masses from the lower crust promote the presenting of some high temperature geothermal fields. And thus, the distribution of fractional melting layers can be lined out according to the range of surface hydrothermal systems.As for the other places, the Tengchong plot lying in the west of Yunnan has the volcanic magma chamber of Quaternary as the heat supply. The West of Sichuan plateau is supplied thermal by intense metamorphism process and tectogenesis.Based on the hydrology geochemistry characteristics of deep fault hot-springs and the law of deep source CO₂ release, the model of deep source CO₂ release is set up in the paper with the theory of the chemistry reaction speed. According to the compartmentalization of Cenozoic conformation cell and the distribution of deep faults in the southwest of china, the quantity release gross of CO₂ is estimated at about 155 thousand ton carbon per year.This paper brings up three conceptional models of hydrothermal systems of CO₂ release in the southwest of China, based on hydrochemistry and isotope geochemistry data.