摘要
解决的问题与研究方法1、解决的科学问题已有研究成果表明:腾冲火山区现今仍有热能和幔源挥发份的大量释放,腾冲火山区地下可能有多个岩浆囊存在,腾冲火山的喷发可能与板块俯冲无关,是局部地幔上隆产生的。但腾冲火山区现代热能和幔源物质释放的强度及其空间分布特征以及与地下岩浆囊的关系,这些岩浆囊的数量、空间分布、几何尺度、温度和活动性以及腾冲火山成因机理的具体模式等问题还没有得到解决。本论文拟尝试解决这些科学问题。2、思路本论文以揭示现今腾冲火山区岩浆活动为目标,以温泉为研究对象,以化学地质温标、同位素示踪、同位素地质温标为手段,依托现代化学和同位素分析测试技术,通过对腾冲火山区温泉逸出气体的大规模采样及成份和同位素分析测试,来研究腾冲火山区现今幔源物质释放场、上地壳温度场和岩浆囊现今温度,并结合前人深部探测、活动监测及成因研究方面的成果,提出腾冲火山孕育喷发的成因机制模型。3、应用的原理火山喷发是地球内部物质和热能向地表释放的一种方式。岩浆在向上运移或滞留在地壳中时,都会对由热传导形成的正常地热梯度造成局部扰动。反过来,正常地热梯度的局部扰动量可以反映岩浆囊的存在。温泉的形成与当地的地热梯度有关,温泉水中溶解的化学物质含量与热储的温度有关。温泉水化学地质温标可以用来揭示其循环深度范围内的正常地热梯度的局部扰动量,从而可以间接反映岩浆囊或其热晕的存在。溶解在岩浆中的气体是火山喷发的驱动力,也是火山岩浆活动的示踪剂。当岩浆向地表上升运移、喷出或在地下冷却结晶时都可释放出气体。气体在火山岩浆运移和喷发中起着重要作用,尤其是在爆炸性喷发中起着支配作用。气体组分和同位素组成资料可用于热力学计算,从而可以研究深部岩浆的物理化学状态。氦气是最稳定、最轻、挥发性最强和扩散渗透能力最强的惰性气体,当岩浆向地表上升运移时,它可以先于岩浆到达地表,因此,在岩浆上侵过程或侵入后的活动过程中,通过对其先行逸出和正在逸出的气体氦同位素组成进行测试,就可以利用其示踪原理确定岩浆的物质来源:对正在上侵的岩浆,应能观测到氦同位素组成的突然变化;对正在或已冷却的岩浆,氦同位素组成的变化会相当的平稳,氦同位素组成值的不同会反映它们的新老程度。来自岩浆的同源共生的CO2-CH4分子间的碳同位素平衡分馏受温度控制,其平衡时间与温度相关。温度越高,平衡时间越短,温度越低,平衡时间越长。平衡时间与平衡温度呈指数关系,高温(比如1000℃)时需要数小时或数天时间量级能达到平衡的在低温时(比如300℃)可能需要百万年的时间量级才能达到新的平衡。因此,当从高温岩浆区上升到地表时,气体的温度是迅速降低的,这使得在高温区达成的同位素平衡在低温区很难被改变,即同位素组成被“冻结”。同位素平衡分馏系数和平衡温度有关,因此通过测试到达地表低温区的CO2-CH4分子间的碳同位素组成,如能判断其同位素交换是平衡的,则可以通过同位素分馏方程来计算平衡温度,而这个温度代表的不是地表再平衡的温度,而是被“冻结”的高温源区温度,即岩浆囊的温度。4、技术路线本论文采取如下技术路线进行研究。首先利用前人已分析过的大量温泉的水化学资料,根据地球化学热力学原理,利用化学地质温标来研究腾冲火山区及其邻近地区的上地壳温度场。温度场可以间接反映岩浆的存在及其活动状况,地热梯度越高,岩浆存在的可能性越大,岩浆活动性越强。研究结果将为利用同位素示踪原理揭示岩浆囊和利用同位素地质温标原理获得岩浆囊温度工作的野外采样设计和实施提供依据。然后利用在腾冲火山区广泛分布的温泉,采集逸出气体为测试对象,分析其常规组分含量和He、Ne的同位素组成。在火山岩区及其外围(如怒江断裂带)的较大范围获取氦同位素组成数据,利用氦同位素3He/4He比值的示踪原理,揭示是否在整个火山区存在一个统一的或几个幔源物质释放中心,这一个或几个幔源物质释放中心则对应一个或几个岩浆囊。在此前提下、利用温度对CO2-CH4的碳同位素平衡分馏的控制原理,通过测试这个或这几个岩浆囊(范围已大大缩小)的CO2和CH4的碳同位素组成,计算这个或这几个岩浆囊的温度。温度越高,岩浆囊的活动性越强。接着,根据本论文的上述观测资料和研究成果,结合前人获得的大地电磁测深、人工地震测深等深部探测资料来佐证岩浆囊的存在,并研究这个或几个岩浆囊的规模及埋深;利用本研究和前人通过20多年积累的幔源物质释放强度的长期观测资料,岩浆囊温度资料,结合前人获得的形变、地震等活动性监测资料研究这个或几个岩浆囊的现今活动性。最后,利用以上观测研究成果,结合前人关于腾冲火山的成因研究成果,提出腾冲火山喷发孕育的机理模型。主要研究内容1、研制防大气污染和具富集功能的野外气体取样器为了保证所采集气体样品不被空气污染,提高观测结果的可信度。同时,为了克服野外采样中诸如温泉气体温度过高、采样空间狭小等原因难以近距离采样,排气规模太小以及CH4需要富集等等一系列问题,研制一套集排气装置、储气装置、微量组份富集装置、样品输出接口装置于一体的气体样品采集器具。2、采集腾冲火山区温泉逸出气体,分析测试这些气体的常规组份和氦氖碳同位素组成用本研究研制的防大气污染采样器采集腾冲火山区温泉逸出气样品,用于常规组分和碳同位素组成分析的气体样品用铝塑气体样品袋装样,用于氦同位素分析的样品用钢瓶或玻璃瓶装样。用气相色谱仪测试常规组分,质谱仪(VG5400)分析3He/4He、4He/20Ne。用本研究研制的防大气污染和具富集功能的采样器采集幔源物质释放强和相对地热梯度高的重叠异常区(岩浆活动区)上方温泉的CO2和CH4气体样品,对CH4碳同位素样品进行现场富集取样,外送分析这些样品的碳同位素组成。3、腾冲火山区上地壳温度场的研究利用前人的温泉水化学分析资料,选用统一地球化学温标,计算热储温度,假定各热储等深,则热储温度与泉口温度之差为相对地热梯度。计算腾冲火山区上地壳的相对地热梯度。通过克里金插值法获得整个腾冲火山区的相对地热梯度平面分布图。根据此空间分布图和数据,研究腾冲火山区上地壳温度场的空间分布特征,探讨与岩浆的存在及其活动性的关系4、腾冲火山区幔源物质释放场研究通过样品的4He/20Ne值对样品的大气污染进行3He/4He矫正,对样品氦同位素组成的源区百分比进行计算,最后对源区百分比进行校正计算。通过克里金插值法获得整个腾冲火山区的原始氦同位素组成3He/4He(Ra)、校正后的3He/4He校正(Ra)以及氦同位素组成地幔源贡献百分比M和校正后的氦同位素组成地幔源贡献百分比M校正的平面分布图。这种图件即能反映出腾冲火山区的幔源物质释放的空间强度水平,同一释放点的时间序列则能反映幔源物质释放的时间变化。结合具体的数据和这些图件,研究腾冲火山区幔源物质释放的时空分布特征,探讨与岩浆的存在及其活动性的关系。5、腾冲火山区岩浆囊现今温度研究对CO2-CH4碳同位素地质温度计的相关文献进行研究,选取最合理的已有平衡分馏方程,或利用最合理的平衡分馏系数数据拟合出最适用的平衡分馏方程,用本研究获得的CO2-CH4碳同位素分馏数据,计算腾冲火山区岩浆囊的的现今温度。6、岩浆的存在及其活动性的综合分析研究根据本论文的上述观测资料和研究成果,结合前人获得的大地电磁测深、人工地震测深等深部探测资料来佐证岩浆囊的存在,并研究这个或几个岩浆囊的规模;利用本研究和前人长期积累的幔源物质释放强度观测资料(20年),岩浆囊温度资料,结合前人获得的形变、地震等活动性监测资料研究这个或几个岩浆囊的现今活动性。7、腾冲火山孕育喷发的成因机制模型研究根据本研究得到的上地壳温度场、幔源物质释放场、岩浆囊温度结果、结合前人大地电磁测深、人工地震测深成果确定目前腾冲火山区现存岩浆囊的数量、空间分布、大小和埋深。然后结合前人通过岩石学和岩石地球化学研究得到的相关成因信息,提出腾冲火山孕育喷发的成因机制模型。主要工作量为了研究目标和上述研究内容的实现,本论文2003年7月开始实施野外观测,2008年5月完成全部研究工作,历时5年。本论文在腾冲火山区及其外围共实施了3期(2003年、2004年、2006年各一期)温泉气体地球化学观测,先后使用车辆4辆,行程16200公里,在63公里半径,12350平方公里的范围内实地考察测量温泉159个次,测量温泉温度145个次,共采集气体样品254个,获得分析测试数据1229个。其中常规组份和CO2碳同位素样品117个,氦氖同位素样品88个,CH4碳同位素样品49个,获得常规气体组份数据724个(96个样品),富集CH4常规气体组份数据181个(21个富集样品),氦氖同位素数据264个(88个样品),CO2碳同位素数据36个(36个样品),CH4碳同位素数据24个(24个样品)。另外搜集与整理了研究区及外围304个温泉的前人温度和水化学成分数据。主要结论通过以上数据的获取和以此为基础对腾冲火山区上地壳温度场、幔源物质释放场及岩浆囊现今温度的研究,结合深部探测、活动性监测和前人的成因研究结果的综合分析,本研究得到如下5点结论:1、腾冲火山区地下现今可能存在3个岩浆囊,第1个岩浆囊位于腾冲县城和清水一带,第2个岩浆囊位于马站和曲石一带,第3个岩浆囊位于五合、龙江、团田和浦川一带。3个岩浆囊上方的上地壳相对地热梯度分别为140℃、120℃、130℃。3个岩浆囊释放挥发物质的幔源比例依次为70%、60%和30%。2、3个岩浆囊的几何尺度(水平方向的直径)可能依次约是20km、19km和23 km(长45km)。3个岩浆囊的埋藏深度不同:第1个岩浆囊位于地下5-25km之间,第2个岩浆囊可能也位于地下10-25km之间,第3个岩浆囊位于地下7-14km之间。3、3个岩浆囊的的现今温度分别为:第1个岩浆囊324-789℃间,平均555℃;第2个岩浆囊402-663℃间,平均532℃;第3个岩浆囊320-1194℃间,平均679℃。可以认为,腾冲火山区地下岩浆囊顶部气体富集区目前的温度变化范围为320-1200℃,岩浆囊的实际温度应高于平均值600℃。三大岩浆囊的边缘温度可能在300-600℃间,中心温度可能在700-1200℃间。4、3个岩浆囊的活动性不同:第1个岩浆囊集相对地热梯度、幔源物质释放、形变和地震活动等异常于一身,岩浆囊正在接受幔源岩浆的补充,活动性最强,直接位于腾冲县城之下,喷发将造成最为严重的损失,需重点监视;第2个岩浆囊的幔源物质释放强度也引人注目,岩浆囊可能也正在接受幔源岩浆的补充,需加强监测;第3个岩浆囊规模大,埋深较浅,幔源物质释放较弱(30%),目前幔源岩浆的补充可能比较微弱,但岩浆囊温度依然较高,需引起注意。5、腾冲火山的形成与现今的板块俯冲无关,是局部地幔上隆引起地壳拉张的结果。地幔上隆的原因可能和古怒江洋壳型岩石圈或/和古密支那洋壳型岩石圈的拆沉有关,但地幔上隆和腾冲火山的喷发远远晚于东西两个古洋壳型岩石圈的俯冲时限,因此可以认为已与严格意义上的板块俯冲作用无关了。腾冲火山区现今幔源物质释放强度的空间分布图象就是这一地幔隆升区空间尺度和隆升强度的最直接反映,上隆区的大小大致为南北长100km,东西宽50km。局部上隆的地幔既为腾冲火山的孕育提供了岩浆物质来源,其产生的地壳拉张也为岩浆的上侵提供了构造通道,这种拉张得到现今本地区地貌和形变观测的支持。主要创新点本论文对腾冲火山的现今活动性这一关键科学问题进行了比较明确的回答,并结合前人通过岩石学和岩石地球化学研究得到的相关成因信息,提出了腾冲火山孕育喷发的成因机制模型,产出了如下4个创新点:1、提出了相对地热梯度的新概念和计算方法,揭示了腾冲火山区上地壳的温度场特征通过对前人温泉基本要素数据的深度挖掘,提出了相对地热梯度的新概念和计算方法。用该概念和方法揭示了腾冲火山区上地壳的温度场特征,发现腾冲火山区上地壳存在3个高于100℃的相对地热梯度异常区。相对地热梯度异常是其下方的岩浆囊的热扩散造成的,可以理解为岩浆囊的热晕(热帽),间接反映了岩浆囊的存在。2、揭示了目前腾冲火山区的幔源物质释放强度的空间分布特征应用氦同位素示踪技术,在东起怒江,西至中缅边境的涵盖整个腾冲火山区的范围内进行了幔源物质释放强度测量。幔源物质释放强度空间分布结果表明,腾冲火山区的幔源物质释放可分强度不同的三个区域。这三个幔源物质释放较强的区域与相对地热梯度研究得到的3个高地热梯度区符合很好,进一步说明腾冲火山区岩浆囊的存在。3、发现目前腾冲火山区存在3个壳内岩浆囊,估计了它们的大小、埋深和现今温度等重要参数,评估了它们的活动性通过对腾冲火山区上地壳温度场、幔源物质释放场的分析研究,结合前人的大地电磁、人工地震等测深结果,发现目前腾冲火山区存在3个壳内岩浆囊。3个壳内岩浆囊的发现为回答腾冲火山现今活动性这一关键科学问题确立了基础。估计了3个岩浆囊的空间尺度和埋深。应用同位素地质温标原理,估算了3个岩浆囊的现今温度。评估了3个岩浆囊的活动性。4、提出了腾冲火山孕育喷发的成因机制模型根据本研究发现的目前腾冲火山区存在3个壳内岩浆囊,结合前人通过岩石学和岩石地球化学研究得到的相关成因信息,提出了腾冲火山孕育喷发的成因机制模型,认为腾冲火山的形成与板块俯冲无关,是局部地幔上隆并引起地壳拉张的结果。腾冲火山区现今幔源物质释放强度的空间分布图象就是这一地幔隆升区空间尺度和隆升强度的最直接反映。局部上隆的地幔既为腾冲火山的孕育提供了岩浆物质来源,也为岩浆的上侵提供了构造通道。
1. QUESTIONS AND METHODS1.1. QuestionsThe existing research results suggest that massive heat energy and mantle-derived volatiles are still releasing present day in theTengchong volcanic area under which more than one magma chambers still exist, and that the Tengchong volcano eruption, possibly not related with the tectonic plate subduction, is resulted from local mantle uplift. But there are some problems unsolved, such as the intensity and the spatial distribution characteristics of heat energy and mantle-derived volatiles release present day in the Tengchong volcanic area, relationship between them and underground magma chambers, and their number, spatial distribution, size, temperature, activities as well as the mechanism model. These are the scientific questions which this dissertation plans to deal with.1.2. Train of thoughtThis dissertation, taking revealing nowadays magmatic activities in the Tengchong volcanic area as a goal, the hot spring as the object of research, chemical geothermometer, isotopic tracer, isotopic geothermometer as the means, based upon the modern chemical and the isotopic analysis technology, adreesses three specific scientific questions: They are the present release field of mantle-derived volatiles, temperature field of the most upper crust and the temperature of nowadays magma chamber of the Tengchong volcanic area. In conjunction with the predecessor’s achievements of deep sounding, the activities monitoring and the origin research, this work proposes a machanism model for the Tengchong volcano generation and eruptions.1.3. PrinciplesThe volcanic eruption is one way by which the earth interior material and the heat energy release to the surface. When magma migrates upward or is detained in crust, the normal geothermal gradient formed by the heat conduction can create the partial perturbation. In turn, partial perturbation quantity of the normal geothermal gradient may reflect the existence of magma chambers. The hot spring formation is related to the local geothermal gradient, and the concentration of chemical substance dissolved in the geothermal water depends upon the temperature of the heat reservior. The hydrochemical geothermometer of a hot spring, can be used to reveal the partial perturbation quantity of the normal geothermal gradient at depth that can penetrate and circulate, thus may reflect existence of a magma chamber or its thermal aureole(or cap) indirectly.The gas dissoluted in the magma is the driving force of volcanic eruption, and is also the tracer of volcano magmatic activity. When migrating to the surface, erupting, cooling or crystallizing in underground media, magma may release gasses. The gasses play an influential role in magma migration and volcano eruption, particularly a dominant role in the explosive eruption. The component and the isotopic composition of gasses, being used for calculating thermodynamic parameters, thus may be sused to study the physic and/or chemical conditions of deep magma cambers.The helium is of stablest, lightest inert gas of which both volatility and proliferation seepage ability are strongest. When magma rises to the surface, the helium may arrive at the surface earlier it. Therefore, during the rising process or active period after being invaded, through analyzing helium isotopic composition of gasses which escaped from it, the mass origin of magma chamber can be determined by using tracing principle of helium isotope: for invading ones, the sudden change of helium isotopic composition ought to be able to observed; for cooling ones, helium isotopic composition should be steady, and their relative ages can be reflected with the specific value of helium isotopic composition.Carbon isotope equilibrium fractionation between homologous paragenetic CO2-CH4 molecular couple from magma chamber is controlled by its temperature to which their equilibrium time is related. The temperature is higher, the equilibrium time is shorter; and the temperature is lower, the equilibrium time is longer. The equilibrium time deponds exponentially upon the reciprocal of the equilibrium temperature. The carbon isotopic equilibration between CO2-CH4 molecular pair at high temperature (for instance 1000℃) which takes order of magnitude of several hours or yaears can attain new re-equilibration at low temperature (for instance 300℃) which needs to take order of 1,000,000 years. Therefore, when rising from the high temperature magma chamber area to the surface, the gasses reduce rapidly their temperatures, for the isotopic equilibrium which achieves in the high temperature area to be very difficult to change in the low temperature area, namely for isotopic composition to be“freezen”. Isotopic equilibrium fractionation factor is related to temperature. Therefore, by analyzing the carbon isotope composition of CO2-CH4 molecular pair at low temperature surface area which arrives at, and if their isotopic exchange equilibration can be judged, then the equilibrium temperature can be calculated through the isotope fractionation equation. It dosen’t represent the temperature at which a new isotopic re-equilibration is attained at the surface, but the“freezen”high temperature of the source area, namely of magma chamber.1.4. Technique approachFirst, using the massive hot spring hydrochemical data that predecessores already have analyzed, according to the geochemical thermodynamics principle, this work studies the temperature field in the most upper crust under the Tengchong volcano and adjacent areas by chemical geothermometer. The temperature field may reflect indirectly existence and activities of magma chambers: the geothermal gradient is higher, the possibility of existence of a magma chamber is bigger, and the activity of magma is stronger. The goal of this work is to obtain the evidence of existence of the magma chamber and the base of the field sampling design and the implementation by which another evidence of existence of magma chamber can be found using the isotopic tracer principle and the today’s temperature of magma chamber can be calculated using the isotope geothermometer principle.Secondly, this work collectes samples of gasses escaped from hot springs which are distributed widespread in the Tengchong volcanic area, analyzes conventional component content and He, Ne isotopic compositions of them. It gains helium isotopic composition data in the wide range of the Tengchong volcano petrographic province and periphery (for example east to the Nujiang fault zone), and using helium isotope 3He/4He ratio tracing principle, promulgates whether there exists unified one or how many mantle-derived mass release centers in entire Tengchong volcanic area. This one or several mantle-derived mass release centers then correspond to one or several magma chambers.Thirdly, under the premise above mentioned, using principle that temperature controls carbon isotopic equilibrium fractionation between CO2 and CH4 molecular pair, through analyzing CO2 and CH4 carbon isotope composition of gasses from hot springs above this one or these magma chanmbers (spacial range already largely narrowed), this work calculates the temperature of this one or these magma chambers. The temperature is higher, the activity of magma chamber is stronger.Then, on the basis of above observed data and the research results of this dissertation above mentioned, it demonstrates the existence of magma chambers, and measures the size and depth of this one or these several magma chambers by unifing deep sounding data that the predecessors obtained by magnetotelluric sounding(MTS) and deep seismic sounding(DSS). It then discusses the nowadays activity of this one or these several magma chambers using observed long-term data of intensity of mantle-derived mass release, that the predecessors and the author of this dissertation have accumulated for more than 2 decades, the data of temperature of magma chambers, to unify the data of the Tenchong volcanic activity from measurements of crust deformation and earthquake monitoring.Finally, it proposes a model for the Tengchong volcanic eruption and origin based on synthesising observation data and research results mentioned above.2. MAIN CONTENTS OF THE THESIS2.1. Developing sample collecting tool for atmosphere-contaminating-prevention with enrichment functionIn order to guarantee that the gas sample collected is not contaminated by the atmosphere so as to improve the credibility of the observation result, and at the same time, to overcome a series of sampling problems in field such as that hot spring gas is of hyperpyrexia, that it is diffculty to collect sample over a short distance because operation space is too narrow, and that it takes a too long time because outgassing is too less, or that certain minor components need to concentrate by chemical reaction, and so on. This research has designed a set of gas sample collection installments which integrate atmosphere exhausting device, gas store device, enrichment device of trace component, the output interface of sample all in one.2.2. Sample-collecting, analysis of conventional and isotopic compositionThis work collectes gas samples escaped from hot springs in the Tengchong volcanic area using the sample collecting instrument with atmosphere-contaminating-prevention and enrichment function. The gas samples which are used to analyze conventional component and carbon isotope composition are packed in aluminum-film-covered plastic bags, the ones for helium isotope compostion analysis are packed in the steel cylinder or glass bottle. With the gas chromatograph it analyzes conventional component, with the mass spectrometer (VG5400) it analyzes 3He/4He, 4He/20Ne. This work collectes CO2 and CH4 gas samples escaped from hot springs in overlaped abnormal areas (magmatically active region), where both the intensity of mantle-derived mass release and relative geothermal gradient are high, using the sample collecting instrument this research developed. This work carries on enrichment to CH4 of the CH4 carbon isotope sample at site, analyzes carbon isotope composition both CO2 and CH4 sample with the mass spectrometer (MAT251).2.3. Analysis of temperature field in upper crust of the Tengchong volcanic areaUsing predecessor's hydrochemical data of hot springs, selecting unified geothermometer, this work calculates the temperature of thermal reservoirs. Assuming that the depth of these thermal reservoirs are same, then the temperature difference between hot springs and thermal reservoirs is defined as relative geothermal gradient. According to this definition, this work calculates the values of relative geothermal gradient in entire the Tengchong volcanic area.Using the values of relative geothermal gradient, the map of relative geothermal gradient in the entire Tengchong volcanic and adjacent areas is obtained with Kriging interpolation. According to this space distribution map and the data, this work studies spatial distribution characteristic of the temperature field of the most upper crust in the Tengchong volcano area, and discusses the relationship between the existence and the activity of magma chambers and the spatial distribution characteristic of the temperature field.2.4. Analysis of spatial-temporal distribution of release of mantle-derived gasAtomsphere contamination correction is made for 3He/4He ratio through the 4He/20Ne value. Then this work calculates percentage proportion of atmosphere, crust and mantle of helium isotope compostion. Finally the correction for percentage proportion of different sources is performed.Using Kriging interpolation, the plane distribution maps of primitive helium isotopic compostion 3He/4He (Ra) ratio values, of corrected helium isotopic compostion 3He/4Hec (Ra) ratio values, of percentage M which express contribution of mantle reservoir to helium isotopic compostion, and of corrected percentage Mc in entire the Tengchong volcanic and adjacent areas are obtained. These maps can reflect the spatial intensity level of mantle-derived mass release in the entire Tengchong volcanic and adjacent areas, and time series of these values of helium isotopic compostion at the same localities can reflect time variations of mantle-derived mass release. Synthesising specific data and these maps, this work studies spacial and temporal distribution characteristics of intensity of mantle-derived mass release in the entire Tengchong volcanic and adjacent areas, discusses the relationship between the existence and activity of magma chambers and these spacial and temporal distribution characteristics.2.5. Calculating of temperature of magma chambersTo search, read and analyze literatures mainly about the thermodynamics principle of isotopic exchange reaction, data of equilibrium fractionation factor and equilibrium fractionation equation of carbon isotope exchange reaction between CO2 and CH4 and temperature range of their utilization, so that this work can select the most appropriate formula and the data explanation principle for this research. Choosing the most resonable equilibrium fractionation equation or formula regressed from carbon isotope equilibrium fractionation factors of CO2 and CH4 which were theoretically calculated or experimentally determined, this work finally calculates the temperature of gas source area (magma chambers).2.6. Integrated analysis of existence and activities of magamsAccording to observed data and the research results of this dissertation mentioned above, unifing deep sounding data that the predecessors obtained by magnetotelluric sounding(MTS) and deep seismic sounding(DSS), it demonstrates the existence of magma chambers, and measures the size and depth of this one or these several magma chambers. It discusses the nowadays activity of this one or these several magma chambers using observed long-term data of intensity of mantle-derived mass release, which this thesis researches and the predecessors have accumulated for more than 2 decades, the data of temperature of magma chambers, to unify the data of Tenchong volcanic activity from crust deformation measurements and earthquake monitoring.2.7. Proposing of model of mechanism of Tengchong volcanoAccording to results on temperature field in upper crust, mantle-derived mass release field, temperature of magma chambers of the Tengchong volcanic area, unifing data of magnetotelluric sounding(MTS) and deep seismic sounding(DSS), this work determines the number, spatial distribution, size and depth of magma chambers which exist present day in the Tengchong volcanic area. Finally, in conjunction with the related information of petrology and the rock geochemistry research, this work proposes a model of Tengchong volcano origin.3. MAIN WORKLOADSIn order to achieve the above research aim and to complete above contents, it taken 5 years for this dissertation to complete the field sample-collecting, analysizing and synthetic research work, from July, 2003 to May, 2008. Field sample-collecting, analysizing for hot spring gas is implemented altogether 3 times in 2003, 2004, 2006, respectively, in the Tengchong volcanic area and the periphery. Employing 4 vehicles successively, traveling 16200 kilometers, We have surveyed 159 hot springs, measured temperature 145 times, altogether gathered 254 gas samples, obtaining 1229 data of chemical and isotopic compostion of them in the range of 12350 square kilometers with the radius of 63 kilometers. Among these samples, 117 are for the conventional component and carbon isotope composition of CO2, 88 for isotope composition of Helium and Neon, 49 for carbon isotope composition of CH4. We have obtained 724 conventional gas component data (of 96 samples), 181 conventional gas component data(of 21 CH4-enriching samples), 264 isotope composition data of Helium and Neon(88 samples), 36 carbon isotope composition data of CO2 (36 samples), 24 carbon isotope composition data of CH4 (24 samples). Moreover we have collected and compiled the numerous data of the temperatures and hydrochemistry ingredient of 304 hot springs in research area and the periphery which analyzed and measuered by fomer investigators.4. MAIN CONCLUSIONSBased on the above data, by resolving theses 3 issues such as temperature field in most upper crust, mantle-derived mass release field, and temperature of magma chamber, and combining achievements in deep sounding, activity monitory and origin research that the former investigators obtained, this research obtains the following 5 conclusions:4.1. There exist 3 magma chambers in crust present day in the Tengchong volcano area. The 1st one is located Tengchong county-Heshun township-Rehai resort area where is in middle of the Tengchong volcano area. The 2nd one is located Qushi-Mazhan where is in northern of the Tengchong volcano area. The 3rd one, lies in Wuhe-Puchuan-Xinhua area where is in southern of the Tengchong volcano area. The relative geothermal gradients of most upper crust above 3 magma chambers are 140℃, 120℃, 130℃, respectively. The mantle-derived proportions of volatile mass release of 3 magma chambers are 70%, 60% and 30%, respectively.4.2. The sizes (the horizontal diameter) of 3 magma chambers are approximately 20km, 19km and 23 km (long 45km), respectively, the depths of them are different: the 1st at 5-25km, the 2nd is 10-25km, and the 3rd is 7-14km.4.3. The temperature of the 1st magma chamber is within 324-789℃, with average 555℃. That of the 2nd, within 402-663℃, with average 532℃, That of the 3rd is within 320-1194℃, with average 679℃. It is believed that variation range of the present temperature of the gas enrichment region which is crown of magma chamber below the Tengchong volcano area is 320-1200℃, the actual temperature of magma chamber should be higher than the mean value 600℃. The temperatures of edge area of these 3 magma chambers possibly are in 300-600℃, the central temperature possibly in 700-1200℃. The nowadays temperatures of these 3 magma chamber’s center has achieved the formation temperature of Rhyolite magma (600-900℃), the Andesite magma (800-1100℃) and basalt magma (1000-1250℃), further suggesting the objective existence of these 3 magma chambers at present in the Tengchong volcano area.4.4. The activities of 3 magma chambers are different. The 1st one, collecting relative geothermal gradient, the mantle-derived mass release, the deformation and the seismic activity and so on abnormal in one, being accepting the supplement from mamtle-derived magma, is of strongest activity, and is located directly under the Tengchong county. Its eruption will cause the most serious losses, and needs the key surveillance. The 2nd one, the release intensity of mantle-derived mass is also noticeable, which is also possibly accepting the supplement from mamtle-derived magma, should be strengthened the monitoring. The 3rd one, which has the biggest size, and is shallowest, where the mantle-derived mass releases is weakest (30%), is possibly accepting weakly the supplement of the mantle-derived magma at present, but with temperature is still very high, must be paid some attention.4.5. The formation of the Tengchong volcano, not related with the tectonic plate subduction, is the result of local mantle uplift which results in crust extension. The local mantle uplift is possibally related with the slab break off of the ancient Nujiang oceanic lithosphere or/and the ancient Myitkyina oceanic lithosphere, But the eruption of Tengchong volcano is far later than the subduction of the two ancient oceanic lithosphere. Therefore it can be considered that the formation of the Tengchong volcano is not related with the normal tectonic plate subduction. The spatial distribution image of mantle-derived mass release intensity present day in the Tengchong volcanic area is the direct reflection of size and strength of this mantle uplift which is 100km long from north to south, 50km wide from west to east approximately. This local uplift mantle either provides matter source of magma for the Tengchong volcano to prepare or resultes in the crust extension which provides structural conduits for magma to migrate up. The crust extension in the Tengchong volcanic area predicted with this model is also supported by today’s local geomorphological investigation and deformation observation.5. MAIN INNOVATIONSThis work has quite explicitly answered the questions about the activity of the Tengchong volcano. Combining the related information which the former investigators obtained by petrology and rock geochemistry research, a model of the Tengchong volcano origin machism is proposed and 5 aspects of innovations are created as follows:3.1. A new concept of relative geothermal gradient is put forward and the temperature field in upper crust of the Tengchong volcanic area is demonstratedBy deeply mining to the predecessor's data of basic elements of hot springs, this work proposed a new concept, the relative geothermal gradient, and its calculation method. It is discovered that there exist 3 abnormal areas where relative geothermal gradient is higher than 100℃in most upper crust in the Tengchong volcano area. The abnormal higher areas of relative geothermal gradient, resulting from thermodiffusion of magma chamber underneath them, may be regarded as thermal aureole(or cap) of magma chamber, and reflects the existence of magma chamber indirectly.3.2. Present day spatial distribution of relesse of mantle-derived gas in the Tengchong volcanic area is demonstratedUsing the isotopic tracer technology, this work carries out survey of intensity of mantle-derived mass release in the region east to Nujiang and west to the Sino-Burman boundary, that covers the entire Tengchong volcano area. The spatial distribution of intensity of mantle-derived mass release in the Tengchong volcanic area suggests that there exist 3 separable different regions where intensity of mantle-derived mass release is abnormally higher. These 3 mantle-derived mass strong release regions overlap on the 3 high relative geothermal gradient areas, further suggestes that there exist magma chambers beneath the Tengchong volcano area.3.3. Three magma chambers are discovered in the Tengchong volcanic area, the important parameters such as sizes, depths and temperatures of them are estimated, and the activities of them are assessedBy analyzing the temperature field in most upper crust, mantle-derived mass release field in the Tengchong volcanic area, unifing data of magnetotelluric sounding and deep seismic sounding, this work discovered that there exist 3 magma chambers in crust present day in the Tengchong volcano area. The discovery of these 3 magma chambers in crust has established the foundation to reply the key scientific question about the nowadays activity of the Tengchong volcano. By synthetic studies, the sizes and depths of these 3 magma chambers are estimated. By appling the principle of isotopic geothermometer, nowadays temperatures have been estimated for these 3 magma chambers. By synthetic studies, the activities of these 3 magma chambers are assessed.3.4. A model of origin mechanism of Tengchong volcano is proposed According to existence of 3 magma chambers which this dissertation discovers in crust in the Tengchong volcano area, combining the related information which the former investigators obtained by petrology and rock geochemistry research, a model of the Tengchong volcano origin machism is proposed. It is considered that the formation of the Tengchong volcano, not related with the tectonic plate subduction, is the result of local mantle uplift which results in crust extension. The spatial distribution image of mantle-derived mass release intensity present day in the Tengchong volcanic area is the direct reflection of size and strength of this mantle uplift. This local uplift mantle either provides matter source of magma for the Tengchong volcano to prepare or resultes in the crust extension which provides structural conduits for magma to migrate up. The crust extension in the Tengchong volcanic area predicted with this model is also supported by today’s local geomorphological investigation and deformation observation.