北秦岭弧前沉积体构造变形及年代学研究

发布时间：2018-01-28 00:01

本文关键词： 北秦岭弧前沉积体构造变形锆石U-Pb定年　出处：《西北大学》2015年硕士论文　论文类型：学位论文

【摘要】：秦岭造山带以商丹缝合带为界分为北秦岭和南秦岭。弧前沉积体位于商丹高应变带以南,以浉鱼嘴-马鞍桥韧性剪切带为界,与南秦岭刘岭群相隔,呈“楔”状嵌入北秦岭构造带。变质砾岩中碎屑锆石数据显示,该区物源全部来自北秦岭,表明该区隶属于北秦岭。岩相学和地球化学的证据表明这套岩石沉积环境为活动大陆边缘。弧前沉积体主要是一套副变质岩。近年来,不少学者对这套岩石的年代学、同位素地球化学以及物源的研究较为深入,并取得了新的认识。但是,人们对这套岩石构造变形的研究则较为缺乏,构造变形期次的划分也较为模糊。研究区紧邻商丹带,区内岩石的构造变形对于商丹带构造演化的约束具有重要的意义。本文通过对弧前沉积体构造变形要素-面理与线理的详细统计、构造样式的精细研究同时配套显微构造分析,并结合前人的工作基础,重新厘定出了两期主要构造变形：早期逆冲推覆、韧性逆冲剪切和晚期左行韧性剪切。两期构造变形的区别主要在野外构造样式上,早期逆冲推覆作用主要形成区域性南倾北倒的置换面理和紧闭褶皱,以及西倾的线理；晚期左行韧性剪切构造样式以透入性发育的糜棱岩带和与之伴生的水平矿物拉伸线理为主。结合前人研究成果分析,第一期构造变形可能为古秦岭洋关闭后南北块体斜向汇聚所致；第二期变形为汇聚晚期陆内走滑剪切的结果。采集该区3件显示左行走滑的糜棱岩样品中,最年轻一期锆石峰值年龄为420Ma,同时结合采集到的侵位于弧前沉积体的最老的辉绿岩脉的年龄(410Ma),将弧前沉积体左形走滑年龄限定在420-410Ma。
[Abstract]:The Qinling orogenic belt is divided into North Qinling and South Qinling by the Shangdan suture belt. The front arc sedimentary body is located south of the Shangdan high strain zone and is separated from the South Qinling Liu Ling group by the Qianyuzui-Ma 'anqiao ductile shear zone. The detrital zircon data in the metamorphic conglomerate show that all the provenances in the area come from the North Qinling Mountains. The evidence of lithofacies and geochemistry shows that the sedimentary environment of this area is active continental margin, and that the front arc sedimentary body is mainly a set of metamorphic rocks. Many scholars have deeply studied the geochronology, isotopic geochemistry and provenance of this set of rocks, and have gained a new understanding. However, the study of the tectonic deformation of this set of rocks is relatively scarce. The division of tectonic deformation stages is also fuzzy. The study area is close to the Shangdan belt. The tectonic deformation of rocks in the area is of great significance to the constraints of structural evolution in the Shangdan belt. The fine study of structural styles is accompanied by microstructural analysis and combined with previous work, two main tectonic deformations have been redefined: early thrust nappe. The difference between ductile thrust shear and late left-lateral ductile shear is mainly in the field tectonic style, and the early thrust nappe mainly forms the replacement surface and closed fold of regional southward tilting and north inversion. And the line of westward inclination; The late Left-line ductile shear structural style is mainly composed of the permeable mylonite belt and the horizontal mineral stretching line associated with it. The first tectonic deformation may be caused by the oblique convergence of the North and South blocks after the closure of the Paleo-Qinling Ocean. The second stage of deformation is the result of late convergent intracontinental strike-slip shear. Among the three samples of mylonite showing left strike-slip, the youngest zircon peak age is 420 Ma. At the same time, the age of the oldest diabase vein transgressive in the pre-arc sedimentary body collected is 410MaA, and the left-shaped strike-slip age of the pre-arc sedimentary body is limited to 420-410Ma.
【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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