东喜马拉雅构造结墨脱剪切带特征及其区域构造意义  

Characteristics of the Medog shear zone in the Eastern Himalayan Syntaxis and its tectonic significance

作　　者：董汉文[1] 许志琴[1] 李源[1] 刘钊[2] 

机构地区：[1]大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京100037 [2]中国地质大学,北京100083

出　　处：《岩石学报》2014年第8期2229-2240,共12页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(1212010818035);国家自然科学基金创新研究群体项目(41221061)联合资助

摘　　要：东喜马拉雅构造结东、西两侧分别为墨脱剪切带和东久-米林剪切带,本文以墨脱剪切带为研究对象,从构造变形几何学和组构运动学方面进行详细研究。结果表明:①剪切带不同部位的变形性质具有逐渐演化的特征,基于产状、变形性质及变质程度等的变化将其从南到北分为三部分:NE走向具右行兼上盘下滑性质的阿尼桥-希让段、近N-S向具右行走滑性质的旁辛-达木段及N(N)W向具右行兼逆冲性质的甘登-加拉萨段;②在墨脱剪切带内识别出两类剪切变形:高温剪切变形和低温剪切变形。除了构造变形及岩相学证据外,石英EBSD组构数据显示区内高温剪切变形以{10■-0}<a>滑移系为主,对应的温度为550~650℃,达到高温角闪岩相,局部(北端和中段)还出现了{10■-0}<c>滑移系,温度更高,大于650℃,相当于下地壳的深度;低温剪切变形以{10■-1}<a>和{0001}<a>滑移系为主,对应的温度小于550℃,即剪切变形发生在绿片岩相或绿片岩相以下的构造环境。结合西界东久-米林剪切带的构造特征,推测在印度板块和欧亚板块碰撞之后,南迦巴瓦变质体受制于这两条剪切带而相对拉萨地体向北推移,并楔入拉萨地体之下。The Eastern Himalayan Syntaxis is bounded by the Medog shear zone in the east and the Dongjiu-Milin shear zone in the west. This paper focuses on the geometry and kinematics of Medog shear zone, which can be further divided into three sections according^to the structure, deformation and metamorphic grade： the NE-SW trending Aniqiao-Xirang normal-sense shear zone, the N-S trending Pangxin-Damu dextral shear zone and the NW-SE trending Jialasa-Gandeng thrust-sense shear zone. Based on structural deformation, petrography and the quartz EBSD fabrics, two patterns of deformation in the Medog shear zone are observed, which are high-temperature and low-temperature deformations, respectively. The study shows that high-temperature deformation is mainly within { 10T0} 〈 a 〉 slip system, with accordant temperature of 550 ～ 650℃ （amphibolite facies）. In addition, { 10i0} 〈 c 〉 slip system was also observed in the northern and middle of the Medog shear zone, which means that the deformation temperature can be even higher than 650℃. The low-temperature deformation is mainly within { 10il } 〈 a 〉 and { 0001} 〈 a 〉 slip systems, which indicate lower temperature of 〈 550℃ and green-schist facies. Combining with the Dongjiu-Milin shear zone, it is suggested that the Namche Barwa metamorphic terrane was constrained by the two shear zones, then moved northward and subducted deeply beneath the Lhasa terrane.

关 键 词：构造变形 石英EBSD组构 墨脱剪切带 东喜马拉雅构造结 

分 类 号：P542.3[天文地球—构造地质学]