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    东昆仑东段东昆中构造带韧性剪切作用及其地质意义

    Ductile shearing in the eastern segment of Central Kunlun tectonic belt and its geological significance

    • 摘要: 东昆仑东段东昆中构造带经历了多期(次)构造事件,现今保留了复杂多样的构造样式。哈图沟、清水泉—塔妥和沟里等地区构造变形十分强烈,且发育有呈NWW-SEE展布的韧性剪切带。通过野外调研及显微构造研究,对东昆中构造带几何学、运动学及动力学等进行了分析,并通过费氏台和EBSD技术对其进行石英C轴组构分析后认为该剪切带为一压-扭性构造界面,且早期为左旋逆冲,晚期为右旋走滑,变形温度为400~550 ℃。对剪切带内的石英亚颗粒及动态重结晶粒度测量计算出研究区内韧性剪切带古应力值约为153.791 MPa。哈图沟牦牛山组变形砾岩(4 个测点)有限应变测量结果显示,越靠近东昆中断裂带砾石Flinn 指数、应变程度、罗德系数(绝对值)越大,且Flinn 指数均大于1,属拉伸变形。结合区域地质资料,认为东昆仑东段东昆中韧性剪切带形成于晚海西—印支期。

       

      Abstract: Multi-stage structural events occurred in central East Kunlun tectonic belt, resulting in complex structural styles which have been preserved up till now.Very intense structural deformation and ductile shear zone exist in Hatugou, Qingshuiquan-Tatuo and Gouli areas, and there is the NWW-SEE ductile shear zone.The authors analyzed the geometry, kinematics and kinetics of the tectonic belt based on field investigation and analysis of microstructure. A quartz C-axis petrofabric analysis on Fedorov and EBSD stage indicates that the shear zone is a pressure- shear structure interface, characterized by left- handed thrust at the early stage, dextral strike- slip at the late stage, and 400~550 ℃ for the deformation temperature.The measurements of sub-grains of quartz and granularity of dynamic recrystallization indicate that the paleostress value is 153.79 MPa for the ductile shear zone in the study area. Furthermore, the closer to the central part of East Kunlun tectonic belt, the higher the Flinn index (>1), the extent of the strain and Lode parameter (absolute value) of gravel, as evidenced by the finite strain measurement of conglomerate (4 points) from Maoniushan Formation in Hatugou, which suggests a tensile deformation. Combined with regional geological data, the authors hold that the eastern segment of central Kunlun ductile shear zone was formed in Late Hercynian and Indosinian.

       

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