【作者】 沈立成；

【导师】 袁道先；

【作者基本信息】 西南大学 ， 自然地理学， 2007， 博士

【摘要】 深大断裂的CO₂释放作用研究是一项非常重要和有意义的工作，它对于确定地球的含碳量，弄清岩溶动力系统、碳的全球地球化学循环过程，大气中CO₂含量增加的原因以及近年来多种并发性灾害的成因都是不可缺少的方面。不仅如此，它也是弄清地幔深部特性和地质过程的重要手段。本文系统地采集了中国西南地区各地温泉水的水化学样品、气体样品及泉华样品、岩石样品，对各类样品进行了有目的的分析。同时对某些项目进行了野外及实验室双重检测。通过对中国西南地区典型温泉的地质背景、环境条件、水化学及碳、氮稳定同位素的分析，探讨了中国西南地区深大断裂出露温泉CO₂释放的一般规律，并进行了初步的释放量计算。根据中国西南地区典型温泉水化学分析结果，结合温泉附近断裂性质及大地构造和小构造特征，对温泉形成条件及泉水水文地球化学特征作出了分析：西藏自治区温泉泉水属中偏碱性，与世界上大多数地热区热水的pH值总貌相似。而在滇西腾冲地块出露的温泉中则存在pH＜4的酸性或强酸泉水。通过多种地球化学指标，比如：硼、铯、锂、氟、矿化度等的分析来说明中国西南地区温泉的出露与大地构造关系紧密，并且在青藏高原腹地存在深部地壳的部分熔融体，而在滇西则存在第四纪火山岩浆房。川西北则主要是多条深大断裂带结合汇合处且有强烈的变质作用决定了CO₂释放。野外实测西南地区各类温泉温度反应地热温度变化范围广。其温度的高低在很大程度上反映了构造活动带的强弱，并与深大断裂相联系、相适应。对于温泉水的补给来源：虽然西南地区各温泉水补给主要是大气降水，同时也不排除存在少量的岩浆岩、变质岩的成岩作用水，及火山岩冷却分异的同生作用水。滇西腾冲火山区所在的腾冲地块位于印度板块与欧亚板块之间，构造活动及地热流活动强烈，存在大量释放CO₂。热海地热区热泉补给水源的多样化，导致热海地热区的水化学特点差异较大。有来自岩浆的分异脱水，同时在该区又存在有大量外源水补给混入的温泉。氮同位素比值极高，几乎存在纯地幔来源。而西藏冈底斯及喜马拉雅带并没有发现第四纪火山，整个藏中至藏南存在异常强烈的水热系统与地壳深部的局部岩浆熔融有关，并从氦同位素分析得到证明，仅有极少量的深源物质混入。川西高原的康定、泸定等地构造位置特殊，是被地质学家称为“中国地质百慕大”的区域。此地亦无第四纪火山的存在，但因为鲜水河断裂带（XSH）与龙门山断裂带（LMS）在此交汇，且属于切穿岩石圈断层，所以碳、氦同位素都显示有深源物质的加入。温泉水化学也存在异常区域，比如硼。中国西南地区CO₂脱气点除会释放大量的CO₂气体以外，还会释放比如N₂、CH₄、He等气体，释放出来的He同位素随所形成的构造部位不同而有不均匀的分布，且与不同的大地构造成因关系密切。自西向东由藏西到藏南至滇西到滇中，R／Ra值呈现由低到高再降低的平面分布规律。氦同位素在空间的分布规律也反映了深源CO₂释放强度的差异。讨论了关于青藏高原腹地地热系统的热源问题“热机效应”，认为是壳内部分熔融层提供热源，并为地下热水加入了大量的热液化学元素。而对于其它区域，比如滇西腾冲地块则由已经存在第四纪火山的浅层岩浆房提供热源。川西则是由变质作用及构造动力摩擦生热提供能量。最后在把握深大断裂出露温泉水文地球化学特征及深源CO₂释放的规律的基础上，运用化学反应速率理论，构建了温泉水热深源CO₂释放模型，并分别计算了已经实地考察的数十个典型温泉的CO₂释放量。利用这些典型温泉以点推广到面，构建了温泉深源CO₂释放强度评价指标体系，对典型温泉作出了释放强度评价。结合大地构造特征——新生代构造单元的划分及中国西南地区主要深大断裂分布，初步估算出中国西南地区CO₂释放量约为15.5万吨／年。在水化学及同位素分析数据的基础上，提出了中国西南地区CO₂释放的三个概念模型。更多还原

【Abstract】 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.更多还原