發(fā)布時間：2018-03-11 08:28

  本文選題：西藏羌塘　切入點：藍嶺　出處：《中國地質(zhì)大學(北京)》2015年碩士論文　論文類型：學位論文

【摘要】：藍嶺地區(qū)位于羌塘中部變質(zhì)雜巖帶,本質(zhì)上為多巖性組成的構(gòu)造增生雜巖帶。石榴子石白云母片巖,作為高壓低溫變質(zhì)雜巖帶的重要組成部分,記錄了俯沖和折返期的各期變形,對研究古特提斯洋的演化有重要意義。本文對藍嶺石榴子石白云母片巖的野外露頭特征、顯微構(gòu)造特征以及超顯微組構(gòu)特征綜合分析,并結(jié)合電子探針成份分析,認為藍嶺石榴子石白云母片巖共經(jīng)歷四期變形和三期變質(zhì)作用。第一期變形為俯沖期的近水平分層剪切,新生面理橫向構(gòu)造置換原生層理,形成透入性的剪切面理及同構(gòu)造石英脈體。隨著俯沖的持續(xù),板塊開始碰撞,形成了第二期變形。這一期變形為近水平擠壓,形成縱向構(gòu)造置換,巖層被強烈擠壓變形,新生面理為緊閉褶皺的軸面劈理,早先面理被強烈置換,發(fā)育無根鉤狀褶皺、石香腸等構(gòu)造。第三期變形為淺層次脆韌性變形,形成于折返中后期,為東西向的擠壓變形,形成區(qū)域上較為寬緩直立的褶皺,巖石中大量形成間隔劈理,疊加于第二期面理之上。第四期變形為地表或近地表環(huán)境下脆性變形,形成于抬升背景下,表現(xiàn)為共軛剪節(jié)理及正斷層。與宏觀變形相對應(yīng),巖石中石英顆粒的顯微構(gòu)造特征同樣保存三期變形證據(jù),第一期變形記錄于石榴子石石英包體中,其晶格優(yōu)選特征顯示石英滑移系為底面a、菱面a,表明為中低溫石英;第二期為高溫變形,由基質(zhì)中高溫石英記錄,這類石英普遍發(fā)育高溫顆粒邊界遷移重結(jié)晶,并發(fā)育高溫滑移系——柱面a、柱面c;第三期變形造成高溫顆粒邊界遷移重結(jié)晶的石英再次低溫膨凸重結(jié)晶,其組構(gòu)特征也出現(xiàn)明顯的由高溫向低溫滑動特征。同時巖石經(jīng)歷了三期變質(zhì)作用,依次為藍片巖相、綠簾角閃巖相以及綠片巖相變質(zhì)。根據(jù)礦物溫壓計計算,巖石的變質(zhì)峰期壓力為1.24GPa,分期溫度在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，

本文編號：1597370