东秦岭丹凤地区丹凤群构造变形和年代学研究对商丹构造带演化的约束

发布时间：2018-07-26 10:10

【摘要】：商丹构造带作为南秦岭和北秦岭地体的分界线,是秦岭洋发生俯冲消减、消亡的主缝合带,是研究中国大陆地质构造的重要区域。商丹构造带主要出露蛇绿混杂岩、混合岩化片麻岩、变质碎屑岩、大理岩、花岗岩体等。丹凤蛇绿岩混杂岩变形特征和变质作用和北侧秦岭群存在显著的区别,岩石建造与商丹带南侧刘岭群具有明显差异,加之野外多期构造变形和多期脉体的侵入成为我们研究古生代以来商丹带构造变形和地质演化的理想区域。本文在全面收集丹凤群野外岩石的构造要素、变形特征和侵入脉体基础上,通过对丹凤群野外变形形迹的分析,厘清了丹凤群内的构造变形期次；对韧性剪切带中糜棱岩和构造片岩根据矿物组合和变形特征进行了应变的测量和变形温度的估算,推断秦岭洋的闭合碰撞方式；此外,除传统的构造变形形迹统计和构造变形解析之外,研究中使用脉体锆石U-Pb方法限定商丹剪切带活动时代。本文还总结前人对秦岭洋俯冲-关闭-陆内造山作用研究成果,而且利用脉体年代学特征试图从秦岭洋演化的角度分析丹凤群在不同演化阶段所表现出的构造变形特征。通过野外地质露头和区域地质背景对商丹构造带中丹凤群蛇绿岩的研究,总结出秦岭洋闭合方向是自东向西逐渐闭合的不规则模式,并结合区域地质特征将丹凤群划分为四个主要阶段：第一期为逆冲推覆(韧性剪切)作用和褶皱作用；第二期区域内主要发生为左行剪切作用,改造早期褶皱。时代在423.2±1.3Ma-410.5±2.3之间；第三期主要为有右行剪切作用,时代在408±2.6Ma-360.6±3.2Ma之间；第四期主要为后期脆性变形的叠加为特征。
[Abstract]:The Shangdan tectonic belt, as the dividing line between the South Qinling and the North Qinling terrane, is the main suture zone for the subduction and subduction of the Qinling Ocean. It is also an important area for the study of the geological structure of the Chinese continent. The Shangdan tectonic belt is mainly composed of ophiolite, migmatite gneiss, metamorphic clastic rock, marble, granite, etc. The deformation characteristics and metamorphism of the Danfeng ophiolite melange are significantly different from those of the Qinling Group on the northern side, and the rock formation is obviously different from the Liu Ling Group on the south side of the Shangdan Belt. In addition, the field multi-period tectonic deformation and multi-period vein intrusion have become the ideal area for us to study the tectonic deformation and geological evolution of the Shangdan belt since Paleozoic. On the basis of collecting the structural elements, deformation characteristics and intrusive veins of the danfeng group in the field, through the analysis of the deformation trace in the field, the tectonic deformation stages in the Danfeng group are clarified in this paper. According to the mineral assemblage and deformation characteristics, the strain measurement and deformation temperature estimation of mylonite and tectonic schist in ductile shear zone are carried out to infer the closed collision mode of Qinling Ocean. In addition to the traditional structural deformation trace statistics and structural deformation analysis, the U-Pb method of vein zircon is used to define the active age of the Shangdan shear zone. This paper also summarizes the previous studies on subduction, closure and intracontinental orogeny in the Qinling Ocean, and attempts to analyze the tectonic deformation characteristics of Danfeng Group in different evolution stages by using the geochronological characteristics of the vein body. Based on the study of ophiolite of Danfeng group in the Shangdan structural belt through field geological outcrop and regional geological background, it is concluded that the closing direction of the Qinling Ocean is an irregular pattern gradually closed from east to west. According to the regional geological characteristics, Danfeng Group is divided into four main stages: the first stage is the thrusting nappe (ductile shear) action and the fold process, and the second stage is the left-lateral shear process, which is the early fold reconstruction. The age is between 423.2 卤1.3Ma-410.5 卤2.3.The third stage is mainly composed of right-line shearing and the age is 423.2 卤2.6Ma-360.6 卤3.2Ma, and the fourth stage is mainly characterized by the superposition of late brittle deformation.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P548

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