西秦岭武山—关子镇地区商丹缝合带构造解析及年代学约束

发布时间：2018-03-11 06:11

  本文选题：西秦岭　切入点：商丹带　出处：《西北大学》2017年硕士论文　论文类型：学位论文

【摘要】：西秦岭武山-唐藏缝合带是秦岭造山带商丹缝合带的西延部分,也是西秦岭地区古生代商丹洋闭合后的遗迹。深入研究商丹带的西延部分对于整体理解商丹缝合带和秦岭造山带乃至中国中央造山系都有着重要的科学意义。在武山-关子镇地区,武山-关子镇蛇绿岩单元和李子园群变火山岩是构成缝合带的主要岩石地层单元,其构造变形、变质记录了洋盆关闭、碰撞造山的地质过程,是研究秦岭造山带古生代大地构造演化的理想场所。本次研究通过分析西秦岭商丹带的野外构造要素和变形特征,将与板块碰撞相关的构造变形划分为三期。其中以右行走滑韧性变形最为显著,表现为在缝合带内部发育的一条韧性剪切带。通过对该剪切带中糜棱岩类的几何学、运动学、显微构造变形、同位素年代学等研究得到了以下主要认识:1.武山韧性剪切带是一条右行走滑剪切带,运动学涡度在0.79-0.99之间,以简单剪切变形为主。2.电子背散射衍射分析结果显示剪切带的微观变形导致石英的多个滑移系活动,包括基面a轴滑移、菱面a轴滑移、棱面a轴滑移和棱面c轴滑移。3.矿物动态重结晶以石英亚晶粒旋转重结晶和颗粒边界迁移重结晶为主,重结晶类型和石英组构反映出变形温度在500℃到650℃之间。4.选取花岗质糜棱岩和侵入剪切带的花岗质岩株进行LA-ICP-MS锆石U-Pb年代学研究,其年龄分别为910 ±4.8 Ma和403 ±3.5 Ma,分别代表了花岗质糜棱岩的原岩和侵入岩的结晶年龄,并且初步限定了剪切带的活动时代。结合区域地质和东秦岭地区(超)高压变质岩石的年代学证据,推断武山韧性剪切带的活动年代应在403-420 Ma之间。5.将东、西秦岭商丹缝合带的构造属性和年代学证据相对比,本研究认为秦岭造山带在加里东期向印支期演化的过程中可能发生了构造体制和动力学背景的转换,商丹缝合带的构造变形性质由古生代的右行走滑剪切变形转变为中生代的左行挤压变形。
[Abstract]:The Wushan-Tang-Tibet suture zone in the West Qinling Mountains is the westward extension of the Shangdan suture belt of the Qinling orogenic belt. It is also a relic of the closure of the Paleozoic Shangdan Ocean in the West Qinling area. Further study of the west extension of the Shangdan Belt is of great scientific significance for the overall understanding of the Shangdan suture belt, the Qinling orogenic belt and even the central orogenic system in China. Wushan-Guanzi Town area, The Wushan-Guanzizhen ophiolite unit and the Liziyuan Group metamorphic rocks are the main lithostratigraphic units forming the suture zone. Their tectonic deformation and metamorphism record the geological process of oceanic basin closure and collision orogeny. It is an ideal place to study the tectonic evolution of the Paleozoic era in the Qinling orogenic belt. In this study, the field tectonic elements and deformation characteristics of the Shangdan belt in the western Qinling Mountains are analyzed. The tectonic deformation associated with plate collision is divided into three stages, of which the right strike-slip ductile deformation is the most significant, as a ductile shear zone developed within the suture zone. Microstructural deformation and isotopic chronology have been studied as follows: 1. The Wushan ductile shear zone is a right strike-slip shear zone with kinematic vorticity ranging from 0.79-0.99. The results of electron backscattering diffraction analysis show that the microcosmic deformation of shear band leads to the movement of many slip systems of quartz, including basic plane a axis slip, rhombohedral a axis slip, rhombohedral plane a axis slip, etc. The dynamic recrystallization of minerals is mainly composed of quartz subgrain rotational recrystallization and grain boundary migration recrystallization. The recrystallization type and quartz fabric reflect the deformation temperature between 500 鈩，

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