羌塘蓝岭地区石榴石白云母片岩变质变形特征研究

发布时间：2018-03-11 08:28

  本文选题：西藏羌塘　切入点：蓝岭　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：蓝岭地区位于羌塘中部变质杂岩带,本质上为多岩性组成的构造增生杂岩带。石榴子石白云母片岩,作为高压低温变质杂岩带的重要组成部分,记录了俯冲和折返期的各期变形,对研究古特提斯洋的演化有重要意义。本文对蓝岭石榴子石白云母片岩的野外露头特征、显微构造特征以及超显微组构特征综合分析,并结合电子探针成份分析,认为蓝岭石榴子石白云母片岩共经历四期变形和三期变质作用。第一期变形为俯冲期的近水平分层剪切,新生面理横向构造置换原生层理,形成透入性的剪切面理及同构造石英脉体。随着俯冲的持续,板块开始碰撞,形成了第二期变形。这一期变形为近水平挤压,形成纵向构造置换,岩层被强烈挤压变形,新生面理为紧闭褶皱的轴面劈理,早先面理被强烈置换,发育无根钩状褶皱、石香肠等构造。第三期变形为浅层次脆韧性变形,形成于折返中后期,为东西向的挤压变形,形成区域上较为宽缓直立的褶皱,岩石中大量形成间隔劈理,叠加于第二期面理之上。第四期变形为地表或近地表环境下脆性变形,形成于抬升背景下,表现为共轭剪节理及正断层。与宏观变形相对应,岩石中石英颗粒的显微构造特征同样保存三期变形证据,第一期变形记录于石榴子石石英包体中,其晶格优选特征显示石英滑移系为底面a、菱面a,表明为中低温石英;第二期为高温变形,由基质中高温石英记录,这类石英普遍发育高温颗粒边界迁移重结晶,并发育高温滑移系——柱面a、柱面c;第三期变形造成高温颗粒边界迁移重结晶的石英再次低温膨凸重结晶,其组构特征也出现明显的由高温向低温滑动特征。同时岩石经历了三期变质作用,依次为蓝片岩相、绿帘角闪岩相以及绿片岩相变质。根据矿物温压计计算,岩石的变质峰期压力为1.24GPa,分期温度在550℃以上。
[Abstract]:The Lanling area is located in the central Qiangtang metamorphic complex belt, which is essentially a multi-lithologic tectonic accretionary complex. The pomegranate Muscovite schist is an important part of the high-pressure low-temperature metamorphic complex belt. The deformation of each stage of subduction and exhumation is recorded, which is of great significance to the study of the evolution of the PaleoTethys ocean. The outcrop characteristics, microstructural characteristics and ultramicro fabric characteristics of the Lanling pomegranate Muscovite schist are comprehensively analyzed in this paper. Combined with electron probe composition analysis, it is concluded that the Lanling pomegranate Muscovite schist has undergone four stages of deformation and three stages of metamorphism. Forming a permeable shear plane and syntectonic quartz vein. With the continuation of the subduction, the plate began to collide and formed a second phase of deformation. The new plane is the axial cleavage of the closed fold, the earlier surface is strongly replaced, and the rootless hook fold, stone sausage and other structures are developed. The third deformation is a shallow brittle ductile deformation, formed in the middle and late period of exhumation, and is an east-west compression deformation. A large number of spaced cleavages were formed in the rocks, which were superimposed on the second plane. The deformation of stage 4th was brittle deformation in the surface or near surface environment, and formed in the uplift background. Corresponding to macroscopic deformation, the microstructural characteristics of quartz particles in rocks also preserve the evidence of three stages of deformation. The first stage deformation is recorded in the garnet quartz inclusion. The characteristics of lattice optimum selection show that the slip system of quartz is the bottom plane a and the rhombohedral plane a, indicating that the quartz is medium and low temperature, the second stage is high temperature deformation, recorded by high temperature quartz in the matrix, this kind of quartz generally develops high temperature grain boundary migration and recrystallization. And developed the high-temperature slip system-cylinder a, cylindrical c; the third stage deformation caused the high temperature grain boundary migration recrystallization quartz again low temperature swelling convex recrystallization, The texture features also show obvious sliding characteristics from high temperature to low temperature. At the same time, the rocks have undergone three stages of metamorphism: blue schist facies, green curtain amphibolite facies and green schist facies. The metamorphic peak pressure of the rocks is 1.24 GPA and the staging temperature is more than 550 鈩，

本文编号：1597370