深部流体对岩石物性的影响及其地震地质意义

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	深部流体对岩石物性的影响及其地震地质意义
	杜建国
	2002
学位授予单位	中国科学院地球化学研究所
学位授予地点	中国科学院地球化学研究所
学位名称	博士
学位专业	地球化学
关键词	岩石物性地震地质地震预测
摘要	中国是地震多发的国家之一,强震常给人民生命财产造成巨大损失.但是,目前人类对地震孕育、发生的机理认识尚浅,进行地震短临预测的水平很低,远不能满足减轻地震灾害的社会需求.因此,有必要对中-强震孕育过程、发生机理以及流体地震前兆等方面进行深入研究.利用矿物岩石地球化学和高温高压实验资料,从微观上研究地球深部介质的化学组成、矿物成份、相态、岩石结构、声波传播速度、电导率等物理化学性质,可以了解流体与深部介质的相互作用以及对岩石破裂、蠕变过程中的作用,反演深部介质的密度、弹性模量,探讨深部孕震介质演化.在震源介质中普遍存在流体,流体在地震孕育过程中起着重要作用.在总结深部流体、高温高压实验研究和流体在地震预测研究进展的基础上,利用高温高压实验技术测定辉长岩和斜长岩高温高压下弹性波速和电导率,结合实验产物的岩组学和微区化学分析结果探讨孕震介质高温高压下物理性质变化的机制;采用气体地球化学方法研究四川西部三个地震带温泉气体的来源及其与地震活动的关系.从震源介质演化和流体地震异常特征方面探讨地震成因和地震预测.
其他摘要	It is necessary to study the genetic mechanics of strong earthquake and the fluid precursors for the shocks because our knowledge about earthquake is so poor that can not meet the social needs of mitigating disaster of strong earthquakes that frequently occurred in China. The advances of the role of deep-earth fluids in earthquake generation, high temperature and high pressure experiments with rocks and the earthquake prediction based on fluid precursors were reviewed in the dissertation. The compression wave velocities (VP) and conductivity (σ) of gabbro and plagioclasite under high temperature and high pressure were measured with the ultrasonic pulse transmission method and impedance spectra technique, respectively. The original and unloaded samples were chemically measured and analyzed with the electron microprobe instrument and observed under the microscope. The mechanisms of VP and o variations of the rocks were discussed based on the data of the experiments and analysis. In addition, the origins of gases in the hot springs and seismological activity in West Sichuan Province were mentioned in the viewpoint of stable isotopic geochemistry. Vp values of the rocks under high pressure decreased with the increase of temperature. However, VP values of different rocks decreased in the different ways. Vp values of the gabbro at the pressure of 1.0 GPa reduced by 4% from the room temperature to 800 ℃, but reduced severely by 16.4% from 800 ℃ to 1100 ℃. VP values of the gabbro at 2.0 GPa reduced 3.6% from room temperature to 850°C, and decreased 4.6% from 850°C to 1000 ℃. Otherwise, Vp values of plagioclasite at 1.0 GPa decreased by 2.2% from room temperature to 680°C, and decreased sharply by 7.6% from 680 ℃ to 880 ℃. The VP value decrease results from mineral dehydration, rock partially-melting under the experiment conditions. The values of conductivity of the rocks at the pressures of 1 and 2 GPa increased with temperature increasing. Under the conditions of 1GP and 410-750 ℃, the conductivity values of plagioclasite are in the range of 10~(-7) S/m to 10~(-5) S/m, and the complex impedance of plagioclasite collected from 12Hz to 105Hz shows only one semicircular impedance arc that represents the conductive mechanism of the grain interior conduction. The experiment data indicated that conductive mechanism of gabbro at temperature less than 680 ℃ was the grain interior conduction, and that the grain boundary conduction occurred at the temperature higher than 680 ℃, which resulted in the increase of conductivity of the rocks. The data of the microscope observation and microprobe analyses argue that no high conductivity grid of interconnection hydrous fluids in the rock was formed during the dehydration, which hints that the formation and evolution of the high conductivity zone in the crust have a close relationship with the amount of the fluids and the interconnection of the fluids as well. The phenomena that the conductivity values of the experiment rocks changed little when the VP values began to decreasing sharply indicated that the grade of minerals dehydration was so lower that the mineral grain boundary and structure of the rock samples changed severely, but did not change the conductive mechanism, which would be the feature of the early stage of a lower-velocity-layer evolution in lithosphere. The stable isotopic geochemical characteristics of helium and carbon of the hot springs indicate that the helium and carbon dioxide in the three earthquake zones of Xianshuihe, Anninghe and Longmenshan in West Sichuan Province have the multiple origins. 3He/4He ratios of the hot springs in Xianshuihe, Longmenshan and Anninghe earthquake zones have the ranges of 0.48-2.59RA, 0.22-1.07 RA and 0.01-0.82 RA, respectively. Higher ~3He/~4He ratios of the hot springs in the Kangding district demonstrate that the helium is partially derived from the mantle, and the helium of the hot springs in the Aninghe and Longmenshan earthquake zones are predominately derived from the crust with mixing of atmospheric helium. δ~(13) C values of carbon dioxide in the researched hot springs range from -17.09‰ to -3.34‰. Carbon dioxide in the free gas samples is isotopicly heavier that that in the water samples. Carbon dioxide from the hot springs in the Xianshuihe earthquake zone is mainly derived from mantle, but carbon dioxide in the Longmenshan earthquake zone is mainly derived from the crust. Helium and carbon dioxide in the hot springs are effective indicators for earthquake activity. The larger values of ~3He/~4He and ~(13)C_(CO2) and geothermal anomaly occurred usually in the more seismological-active region. The main source of geothermal reservoirs in the researched earthquake zones is the mantle heat that is carried by upward migration of mantle fluids. Deep-earth fluids play an important role in the earthquake generation besides of reducing the friction stress between the fault blocks. Due to a lot of heat must be carried to the crust when the mantle fluids migrate upward, explosion would occur when the porous pressure and thermal stress in the region where deep-earth fluids accumulate exceed the stress threshold of the surrounding rocks, which would be a kind of genetic mechanism of earthquake. The classic examples for this mechanism are the earthquakes occurred in the geothermal and volcanic regions. It could be concluded that the middle and deep earthquakes may be genetically explained by this mechanism. Nevertheless, our knowledge about the interior of the earth and earthquake generation is limited. More work would be done to explain earthquake generation and to forecast earthquake in a short term by means of geochemistry.
页数	47
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3700
专题	研究生_研究生_学位论文
推荐引用方式 GB/T 7714	杜建国. 深部流体对岩石物性的影响及其地震地质意义[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,2002.

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