西藏南部仲巴微地体脆—韧性剪切带变形特征分析
发布时间：2018-07-13 17:30
【摘要】：“仲巴微地体”位于雅鲁藏布江构造带西段,内部发育普遍产生变形变质的奥陶系-三叠系地层,在志留-二叠系接触部位发育一条的走向NWW的脆-韧性剪切带,宽200-1000m,长数十公里,总体倾向190°-220°,倾角在20°-40°之间,由南向北变形逐渐减弱。通过对仲巴微地体脆-韧性剪切带野外调查及室内显微构造分析,结合EBSD分析及构造解析方法,对仲巴微地体脆-韧性剪切带进行了较为详细的研究,初步得出了以下几方面的认识:(1)发育在脆-韧性剪切带内的糜棱岩中面理的总体倾向朝南,剪切带内糜棱岩发育拉伸线理,可见眼球状碎斑、压力影、不对称小褶皱、书斜、劈理折射等宏观构造;变形岩石显微镜下可见石英、方解石波状消光,机械双晶、眼球状构造、扭折等显微构造现象,石英、方解石颗粒重结晶作用明显,多为动态重结晶作用;以石英膨凸重结晶、亚颗粒旋转重结晶为主,见少量方解石静态重结晶;(2)在动力学方面,通过分形法计算得出研究区脆-韧性变形温度范围为330℃~570℃,古应力差值介于46.32~74.78MPa之间,应变速率介于8.03×10-13s-1~1.41×10-11s-1之间。(3)石英、方解石EBSD组构分析结合矿物变形温度计可知仲巴微地体脆-韧性剪切带中典型矿物的变形分为三个阶段:由中高温时期的右行剪切→中低温时期的左行剪切→低温时期的左行剪切,变形温压环境是从高绿片岩相到低角闪岩相的变质环境→低绿片岩相的变质环境。(4)根据EBSD分析结合研究区构造背景,认为该脆-韧性剪切带的形成与特提斯洋向北俯冲作用相关,并经历了印度板块与欧亚板块的碰撞与青藏高原差异性隆升阶段,这三次大型的构造活动均造成了该剪切带不同程度的剪切滑动。由俯冲带前缘强烈挤压,侧向伸展剪切形成顺层剪切,导致了脆-韧性剪切带的形成,在印度板块与欧亚板块的碰撞阶段,由碰撞-陆内继承性收缩挤压形成了北东-南西、近南北向挤压,此时剪切带滑动性质为挤压型剪切滑动,之后伴随青藏高原南部隆升,脆-韧性剪切带的再一次滑动。
[Abstract]:The "Zhongba micro-terrane" is located in the western section of the Yalu Zangbujiang structural belt. The Ordovician and Triassic strata are generally developed in the interior, and a brittle-ductile shear zone with strike NWW is developed in the Silurian and Permian contact area. Its width is 200-1000m, its length is tens of kilometers, the general tendency is 190 掳-220 掳, the inclination angle is between 20 掳-40 掳, and the deformation gradually weakens from south to north. The brittle-ductile shear zone of Zhongba micro-ground is studied in detail by field investigation and laboratory microstructure analysis, combined with EBSD analysis and structural analysis. The main conclusions are as follows: (1) the general tendency of the surface of mylonite developed in the brittle ductile shear zone is southward, and the mylonite in the shear zone develops stretching lines, with eyeball patches, pressure shadows, asymmetrical small folds, and diagonal. Microstructural phenomena such as cleavage refraction, quartz, calcite wave extinction, mechanical double crystal, eyeball structure, torsion and so on, quartz and calcite particles recrystallization can be seen under the deformed rock microscope. Most of them are dynamic recrystallization, quartz swelling and convex recrystallization, subparticle rotation recrystallization, and a small amount of calcite static recrystallization. (2) in kinetic aspect, the brittle ductile deformation temperature range of 330 鈩，
本文编号：2120182
[Abstract]:The "Zhongba micro-terrane" is located in the western section of the Yalu Zangbujiang structural belt. The Ordovician and Triassic strata are generally developed in the interior, and a brittle-ductile shear zone with strike NWW is developed in the Silurian and Permian contact area. Its width is 200-1000m, its length is tens of kilometers, the general tendency is 190 掳-220 掳, the inclination angle is between 20 掳-40 掳, and the deformation gradually weakens from south to north. The brittle-ductile shear zone of Zhongba micro-ground is studied in detail by field investigation and laboratory microstructure analysis, combined with EBSD analysis and structural analysis. The main conclusions are as follows: (1) the general tendency of the surface of mylonite developed in the brittle ductile shear zone is southward, and the mylonite in the shear zone develops stretching lines, with eyeball patches, pressure shadows, asymmetrical small folds, and diagonal. Microstructural phenomena such as cleavage refraction, quartz, calcite wave extinction, mechanical double crystal, eyeball structure, torsion and so on, quartz and calcite particles recrystallization can be seen under the deformed rock microscope. Most of them are dynamic recrystallization, quartz swelling and convex recrystallization, subparticle rotation recrystallization, and a small amount of calcite static recrystallization. (2) in kinetic aspect, the brittle ductile deformation temperature range of 330 鈩，
本文编号：2120182
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