大巴山构造带构造脉体特征及其形成机制

发布时间：2018-03-08 04:26

本文选题：大巴山构造带　切入点：地质流体　出处：《长安大学》2015年硕士论文　论文类型：学位论文

【摘要】：大巴山构造带位于四川盆地北缘,秦岭造山带中段南侧,地处秦岭构造带与下扬子地块的交接部位。通常以城口—房县断裂和铁溪—巫溪隐伏断裂为界,将大巴山构造带自北向南依次分为北大巴山逆冲—推覆构造带、南巴山前陆弧形冲断褶皱带(大巴山前陆构造带)以及大巴山前陆坳陷带(四川盆地东北部)三个次级构造单元。野外地质调研发现,大巴山构造带内的构造脉体发育十分普遍,且不同次级构造单元内发育的脉体特征不同,通过对脉体的野外宏观观察及室内显微镜下分析,对其进行了期次划分,分别为:第一期构造脉体为揉皱脉体,脉体普遍发生了变质、变形现象,主要分布于北大巴山逆冲—推覆构造带内,发育于古生界地层中,为前印支期地质流体的产物;第二期构造脉体为X型剪裂隙充填脉,脉体未发生变质作用,主要分布于北大巴山逆冲—推覆构造带和大巴山前陆构造带内,发育于古生界和三叠系地层中,为印支期同构造流体的产物;第三期构造脉体为张裂隙充填的脉体,脉体平直且比较干净,在整个大巴山构造带内的前白垩系地层中均有分布,为燕山期同构造流体的产物。分别采集不同期次的构造脉体及其围岩样品,进行了碳氧同位素、氢氧同位素和微量稀土元素地球化学分析,指示了三期构造脉体均形成于开放的氧化环境中,其物质来源主要为围岩碳酸盐岩活化、重结晶以及大气降水的溶解作用。脉体形成时的流体主要为建造水,该建造水是由大气降水沿地层裂隙流动时与围岩碳酸盐岩发生水岩反应形成的。运用构造解析的方法分别对第二期和第三期构造脉体进行了应力场分析,证实了第二期脉体为印支末期近南北向构造挤压应力场下形成,第三期构造脉体形成于燕山期的近东西向构造运动中。对第三期脉体的几何特征(宽长比)和空间分布特征(产状)进行了统计,推算出第三期构造脉体形成过程中的应力比(?=(σ2-σ3)/(σ1-σ3))、驱动应力比(R’=(Pf-σ3)/(σ1-σ3))和流体超压(Δsi=Pf-σ3),计算得到?=0.452,R’=0.313,反映了流体压力小于中间主应力,而计算出的流体超压Δsi可达到167Mpa,说明了第三期构造脉体形成时存在有异常高压流体,且这种高压流体可能是由燕山构造运动造成。
[Abstract]:The Dabashan tectonic belt is located in the northern margin of Sichuan Basin and the south of the central Qinling orogenic belt. It is located at the junction of the Qinling tectonic belt and the lower Yangtze block. The boundary is usually the Chengkou Fangxian fault and the Tiexi-Wuxi hidden fault. The Dabashan tectonic belt is divided from north to south into the North Dabashan thrust-nappe tectonic belt. Three secondary tectonic units of the South Bashan Foreland Arc thrust fold Belt (Dabashan Foreland tectonic Belt) and the Dabashan Foreland Depression Zone (northeast Sichuan Basin). The development of tectonic veins in the Dabashan tectonic belt is very common, and the characteristics of veins developed in different secondary tectonic units are different. Through the field macroscopical observation of the veins and the analysis under the laboratory microscope, the stages and stages of the veins are classified. They are as follows: the first stage of tectonic vein body is crinkle vein body, the vein body has metamorphosed and deformed generally, mainly distributed in North Dabashan thrust-nappe tectonic belt, developed in Paleozoic strata, is the product of pre-Indosinian geological fluid; The second stage of tectonic vein is X-type shear fissure filling vein. The vein body has no metamorphism and is mainly distributed in North Dabashan thrust-nappe tectonic belt and Dabashan Foreland tectonic belt, and developed in Paleozoic and Triassic strata. It is the product of the same tectonic fluid of Indosinian epoch, the third tectonic vein is filled with extensional fissure, the vein body is straight and clean, and it is distributed in the pre-Cretaceous strata in the whole Dabashan tectonic belt. The samples of tectonic veins and their surrounding rocks were collected in different periods of Yanshanian period, and the carbon oxygen isotopes, hydrogen and oxygen isotopes and trace rare earth elements were analyzed. It is indicated that the three tectonic veins are formed in an open oxidation environment, and their material sources are mainly from the activation of the surrounding rock carbonate rocks, recrystallization and the dissolution of atmospheric precipitation. The formation water is formed by the reaction of water and rock to the carbonate rock of surrounding rock when the precipitation flows along the formation fissure. The stress field of the second and third tectonic veins is analyzed by the method of structural analysis, respectively. It is confirmed that the second vein body was formed under the compressive stress field of the late Indosinian near south-north direction. The third tectonic vein was formed in the near east-west tectonic movement of Yanshanian epoch. The geometric characteristics (width to length ratio) and spatial distribution (occurrence) of the third stage vein body were statistically analyzed, and the stress ratio during the formation of the third stage tectonic vein body was calculated. (蟽 2- 蟽 3 / (蟽 1- 蟽 3), driving stress ratio = Pf- 蟽 _ 3 / (蟽 _ 1- 蟽 _ 3) and fluid overpressure (螖 sig Pf- 蟽 _ 3), calculated? The results show that the fluid pressure is smaller than the intermediate principal stress, and the calculated fluid overpressure 螖 si can reach 167Mpa.This indicates that there is an abnormal high pressure fluid during the formation of the third tectonic vein, which may be caused by the Yanshanian tectonic movement.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P542

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