大巴山陆内造山带高压古流体及其运移动力学机制研究  

High pressure paleofluid in the Dabashan intercontinental orogenic belt and its migration dynamics

作　　者：覃小丽[1,2] 李荣西[1,2] 杨玲 董树文[4] 何为[5] 杨清宇[5] QIN Xiaoli LI Rongxi YANG Ling DONG Shuwen HE WeiS YANG Qingyu(School of Earth Science and Resources, Chang＇an University, Xi ＇an 710054, China Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, Ministry of Land and Resources, Xi＇an 710054, China Shaancci Institute of Geological Survey, Xi＇an 710065, China Chinese Academy of Geological Sciences, Beijing 100037, China Exploration Department of PetroChina Changqing Oil field Company, Xi＇an 710021, China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]国土资源部岩浆作用成矿与找矿重点实验室,陕西西安710054 [3]陕西省地质调查院,陕西西安710065 [4]中国地质科学院,北京100037 [5]中国石油长庆油田分公司勘探部,陕西西安710021

出　　处：《地学前缘》2017年第2期123-129,共7页Earth Science Frontiers

基　　金：国家自然科学基金项目(41173055;41602128);中央高校基金项目(310827151062)

摘　　要：陆内造山带普遍存在的高压流体与金属矿产与油气形成与分布关系十分密切。大巴山陆内造山带发育有大量同构造期方解石脉,碳氧同位素反映其为围岩碳酸盐岩成岩流体产物。通过对方解石脉中盐水包裹体分析测试,应用包裹体p-T-X相图确定的大巴山构造带同构造期古流体压力自北而南由高变低,即从大巴山逆冲构造带、大巴山前陆构造带到大巴山前陆坳陷古流体压力分别为240~270 MPa、220~240 MPa和170~190 MPa,而恢复的古流体压力梯度分别为2.2 MPa/100m、2.3 MPa/100m和2.0 MPa/100m,明显高于正常静水压力,表明大巴山陆内造山期古流体为典型异常高压流体。综合分析表明,大巴山陆内造山带和四川盆地自古至今普遍存在异常高压流体。结合区域地质研究认为,处于大巴山推覆体前缘、受志留系泥岩滑脱层和逆掩断层控制的高压体系具有压力封存箱特征。大巴山陆内造山带高压流体是在埋藏过程中形成的,其形成深度在2 800m左右,异常高压是大巴山构造带驱动流体迁移的主要动力之一。High pressure paleofluid,widely existed in the intra-continental orogenic belt,had a close relationship with the formation and distribution of metal minerals and oil/gas.A great number of syntectonic calcite veins were found in the Dabashan intra-continental orogenic belt.The carbon and oxygen isotope analysis of calcite veins indicate they were diagenetic product from the carbonate wall rock.Based on the analysis of brine inclusions contained in calcite veins,the p-T-X phase diagram of brine fluid inclusion was used to determine the paleofluid pressure represented by syntectonic calcite veins.The paleofluid pressures were 240-270 MPa,220-240 MPa and 170-190 MPa in Dabashan thrust belt in the north,Dabashan foreland in the middle and Dabashan foreland depression（Sichuan Basin）in the south,respectively;whereas the pressure gradients were 2.2 MPa/100 m,2.3MPa/100 mand 2.0MPa/100 m,respectively,much higher than that of hydrostatic fluid supporting the notion that syntectonic paleofluid is typical abnormal high pressure fluid.Comprehensive analysis shows abnormal high pressure paleofluid had been widely existed in the Dabashan orogenic belt and Sichuan Basin.Combined with regional geology,it is proposed that the pressure compartments lie in front of the Dabashan nappe and were controlled by the Silurian slip mudstone layer and overthrust fault.The high pressure fluid was generated during the burial process at a depth of about 2800 m,demonstrating that the abnormal high pressure is one of the main forces in driving paleofluid migration in the Dabashan tectonic belt.

关 键 词：方解石脉 流体包裹体 压力梯度 陆内造山 大巴山构造带 

分 类 号：P542.2[天文地球—构造地质学]