【作者】 高婷；

【导师】 徐学义；

【作者基本信息】 长安大学 ， 构造地质学， 2011， 硕士

【摘要】 西秦岭造山带是我国重要的地质单元之一,其构造位置特殊且经历了复杂而又漫长的地质构造演化过程。西秦岭西段北部花岗质岩浆作用发育,是我国重要的金多金属成矿省之一。研究西秦岭北段花岗岩浆作用的形成时代、岩石地球化学特征及形成构造环境,对于认识西秦岭中生代构造演化过程,指导区域地质找矿部署具有重要理论和现实意义。以往针对西秦岭地区的花岗岩浆作用研究大多集中在西秦岭的东段地区,而西秦岭西段北部的花岗岩的研究程度相对较低。本论文主要通过西秦岭西段北部重要花岗质侵入体年代学和主量、微量元素及同位素地球化学的研究,建立花岗岩形成的年代学格架,探讨其形成构造环境和岩石成因,分析花岗岩与成矿作用关系,为区域地质找矿工作部署提供信息。论文获得一批西秦岭花岗岩高精度LA-ICPMS锆石U-Pb年龄数据,结合前人研究成果,认为西秦岭西段北部花岗岩浆作用自中二叠纪晚期264Ma就开始,大规模的花岗岩浆活动从早三叠世开始,到晚三叠世末期200Ma结束。五个重要花岗岩体的岩石学、地球化学研究表明,西秦岭西段以中酸性侵入体为主,岩石类型主要以花岗闪长岩、二长花岗岩和花岗岩、碱长花岗岩等为主；花岗质岩体多数具有埃达克岩的特征,部分具有喜马拉雅型花岗岩的特征。花岗岩锆石Hf同位素研究表明花岗岩主要为地壳部分熔融的产物,其中地壳源区的成分包含了古元古代地壳和中元古代地壳的组分。综合前人同位素示踪研究成果,认为西秦岭地壳基底具有扬子型块体的构造属性。花岗岩的埃达克岩和喜马拉雅型地球化学特征显示花岗岩形成于地壳加厚构造环境。综合本次研究和区域地质特征,认为三叠纪时西秦岭地区为陆内叠覆造山阶段,在二叠纪末-三叠纪时期,地质演化总体为陆陆俯冲-叠覆期,陆壳加厚并发生部分熔融,形成了具有埃达克岩和喜马拉雅型的地球化学特点的花岗岩浆作用。提出西秦岭埃达克岩和喜马拉雅型花岗岩与金铜多金属成矿作用关系密切,分析了埃达克岩和喜马拉雅型花岗岩富集金铜等成矿元素的机理,结合成矿模式分析,提出围绕着区内的埃达克质岩以及喜马拉雅型花岗岩找矿开展工作部署的思路。更多还原

【Abstract】 Western Qinling orogenic belt is an important geological unit in China and the belt has undertaken a long and complicated geological tectonic evolution. Granite magmatism developed in the north part of west segment of western Qinling mountain area which is one of the important polymetallic deposits. The study on chronology, geochemistry and tectonic environment of the granite magmatism in north area of Western Qinling show theoretical and practical significance for understanding the tectonic evolution of western Qinling in Mesozoic and guiding the deployment of regional geological prospecting work.Previous researches about granite magmatism in Western Qinling are mainly focused in the east segment, but the study on granite in the west area is a little deficient. By the researth on chronology, major and trace elements, and isotope geochemistry of important granitic intrusions in study area, this paper set up the temporal and spatial evolution framework of granite, discuss the tectonic setting and petrogenesis, analyze the relationship between granite and mineralization, and provide information for the deployment of regional geological prospecting work. Five groups of LA-ICPMS zircon U-Pb dating data of granite in study area have been got. Combined with previous research achievements, we consider that the granite magmatic activity began from 264Ma, the latest period of middle Permian about 200Ma. The large-scale movement of magma occurred between early Triassic and late Triassic.The study on petrology and geochemical of 5 important intrusions show that there mainly are middle-acid intrusions and mostly granodiorite, monzogranite, granite and alkali feldspar granite in the west segment of Western Qinling. The most intrusions show the characteristics of Adakite, some Himalaya type. The Hf isotope data suggests that the granite has crust source including Paleoproterozoic crust and Proterozoic crust. Based on previous isotope researches, we consider that the basement of Western Qinling indicate the tectonic attribute of Yangzi block.The characteristics of Adakite and Himalaya-type show that the granite formed when crust became thicken. Combined with regional geology, we consider that in Triassic period the Western Qinling area are in continental stacking orogeny stage. There are continent- continent collision and overlay stage in late Permian- Triassic period, continental crust became thicken and partial melting, then formed granite magmatism with characteristics of Adakite and Himalaya-type.This paper points that the formation of gold-copper polymetallic mineralization related closely to the Adakite and Himalaya-type granite in Western Qinling. The enrichment mechanism of gold-copper et al has been analyzed. Combined with mineralization pattern analysis, the idea of carring out work plan around the prospecting in Adakite and Himalaya-type granite in study area has been proposed.更多还原