班公湖—怒江缝合带改则地区构造特征及构造演化

发布时间：2018-06-02 01:25

本文选题：班公湖—怒江缝合带 + 改则地区　；参考：《成都理工大学》2015年硕士论文

【摘要】：班公湖—怒江缝合带是青藏高原内部一条极为重要的地质界线,分隔了两侧的羌塘地块和拉萨地块,并保留着中、新特提斯洋演化的重要信息。目前对班公湖-怒江洋盆的性质、演化模式、俯冲极性和闭合机制等关键的大地构造问题都存在着激烈争论,这直接影响了对班公湖—怒江缝合带构造演化的理解。本文通过1:5万、1:1万地质填图及野外露头构造详细解析,对研究区构造期次进行划分。在已有的地质调查和研究基础之上,以岩石学、岩石地球化学为基础,以同位素年代学研究为主线,采用地质学、地球化学、同位素年代学等多学科结合的研究方法,查明班公湖—怒江缝合带中西段改则地区的火山、岩浆岩的形成时代、构造环境,依此确定洋盆不同阶段的存在时限,演化特征。初步研究表明:(1)由于经历班怒洋长期复杂的开合演化并遭受后碰撞期火山岩断陷盆地叠加以及印-亚大陆碰撞高原隆升期强烈的构造改造,展现出区块分隔、南北分带、东西分段和垂向分层的构造格局。研究区处于泛华夏大陆晚古生代羌塘-三江造山系的班公湖-双湖-怒江-昌宁对接带(I级大地构造单元)南侧。II级构造单元划分以打格弄-扎茬亚-尼布断裂为界,北部属南羌塘增生弧盆地(II),南归班公湖-怒江洋结合带。(2)研究区主要经历了三期构造变形:第一期变形(D1)与班公湖—怒江缝合带同造山挤压事件有关,主要表现为近S-N向构造挤压作用力下(包含NW-SE向)形成了区域上近E-W向构造带,以发育透入性的S1面理为标志。第二期构造变形(D2)与晚造山期近N-S向挤压左旋挤压事件相关,主要表现以蛇绿岩带中S1左旋剪切面理以及沙木罗组(J3K1s)中不对称倾竖褶皱和斜歪褶皱为标志,形成了区域性的轴面劈理S2。第三期构造变形(D3)与后造山期近N-S向(包含NE-SW向)右旋挤压事件相关,主要表现以以蛇绿岩带中S2右旋剪切面理、色哇组右旋剪切面理、日干配错组中右旋走滑背景下的局部左旋不对称倾竖褶皱以及去申拉组中近东西向与近SN向宽缓褶皱叠加以及褶皱轴向的向南偏转为标志,在色哇组中形成了轴面劈理S2。(3)综合研究区的地层学、岩石学、地球化学、年代学和构造地质记录分析,研究区构造地质演化经历了4个演化阶段:①班公湖-怒江洋扩张阶段(P-T1),通过对第I类高压榴辉岩的研究结果表明班公湖—怒江洋盆的裂解时间至少可以提前至晚二叠世—三叠纪;②班公湖-怒江洋俯冲和高压变质岩折返阶段(T2-J2),通过对第II类高压榴辉岩的研究结果表明至少在早侏罗世班公湖—怒江洋盆已经开始俯冲,将俯冲的下限时间延至早侏罗世;③班公湖-怒江洋闭合和碰撞造山阶段(J3-K1);④后碰撞阶段(K1至今),通过对去申拉组两件火山岩进行同位素U-Pb年龄分析表明其加权平均年龄为106.7±0.7 Ma和106.0±0.8 Ma,时代为早白垩世晚期,形成的构造环境为大陆板内裂谷,代表洋盆碰撞后陆内伸展阶段形成的火山岩。
[Abstract]:The ban Gong Lake Nu River suture zone is a very important geological boundary inside the Qinghai Tibet Plateau, which separates the Qiangtang and Lhasa blocks on both sides, and maintains important information on the evolution of the new Tethys ocean in the middle of the Qinghai Tibet Plateau. At present, the key geodetic problems such as the nature, evolution model, subduction polarity and closed mechanism of the ban Gong Hu Nu River oceanic basin are all stored. In the intense debate, this directly affects the understanding of the tectonic evolution of the ban Gong Lake - Nu River suture zone. This paper, through the detailed analysis of the 1:5 million, 1:1 million geological mapping and outcrop structure, divides the tectonic period of the study area. Based on the existing geological survey and research, it is based on petrology, rock geochemistry and isotopic years. As the main line of study, the study methods of geology, geochemistry and isotopic chronology have been used to find out the volcano in the region of the middle and western section of the Nu River suture zone, the age of the formation of magmatic rocks, the tectonic environment, and the time limit and the evolution characteristics of the different stages of the oceanic basin. The long and complex evolution of the banyan ocean and the tectonic transformation of the volcanic rock fault basin in the post collision period and the uplift period of the collision plateau of India and Asia, show the structural pattern of the partition, the South and the north, the East and the West and the vertical stratification. The study area is in the Bangong of the Qiangtang Qiangtang Sanjiang orogenic system of the late Paleozoic in Pan Hua Xia continent. The.II level tectonic units on the south side of the lake double Lake Nu River Changning docking zone (I grade tectonic unit) are divided on the southern side of the TG Nong Zhan Nibu Nibu fault, the northern part of the South Qiangtang accretive arc basin (II), the Bangong Lake and the Nu River ocean zone in the south. (2) the study area has undergone three stages of deformation: the first phase deformation (D1) and the Bangong Lake Nu River suture zone Related to the orogenic extrusion event, it is mainly shown that the near S-N tectonic compression force (including NW-SE direction) has formed a regional near E-W direction structure zone, which is marked by the development of the permeable S1 surface texture. The second phase tectonic deformation (D2) is related to the late orogenic period near N-S compression left lateral extrusion event, mainly manifested by the S1 left-handed shear surface in the ophiolite belt. As well as the asymmetrical tilting fold and skew fold in the J3K1s, the regional axial cleavage S2. third phase structural deformation (D3) is related to the near N-S direction (including NE-SW direction) dextral extrusion events in the post orogenic period, mainly manifested in the S2 right rotation shear surface in the ophiolitic zone, the dextral shear surface of the Shah wow group and the diurnal error group. The local left-hand asymmetrical vertical folds in the middle dextral strike slip background and the superposition of the near east-west and near SN wide slow folds in the Deshen group and the southward deflection of the fold axis are marked. The stratigraphy, petrology, geochemistry, geochronology, geochronology, geochronology, geochronology, and tectonic geological records are formed in the shaxa group in the Shah wow group. The geological evolution of the study area has undergone 4 stages of evolution: (1) the bandgong Lake Nu River ocean expansion phase (P-T1). The results of the study of class I high pressure eclogite show that the splitting time of the bandgong Lake - Nu River ocean basin can be at least to the Late Permian Triassic Period; (2) the bandgong Lake - Wrath Jiang Yang subduction and the high pressure metamorphic rock reentry phase (T2-J2). The results of the study on the type II high pressure eclogite show that at least the early Jurassic band Gong Lake Nu River ocean basin has begun subduction, extending the subduction time to the early Jurassic; (3) the ban Gong Lake Nu River ocean closure and the collision orogenic stage (J3-K1); (4) the post collision stage (K1 today), through the isotopic U-Pb of two volcanic rocks in the Deshen group The age analysis shows that the weighted average age is 106.7 + 0.7 Ma and 106 + 0.8 Ma, and the era is late Early Cretaceous, the tectonic environment formed in the continental plate rift, representing the volcanic rocks formed during the intracontinental extension of the ocean basin.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P548

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