西藏纳木错西蛇绿岩成岩成矿作用

发布时间：2018-01-07 08:24

本文关键词：西藏纳木错西蛇绿岩成岩成矿作用　出处：《成都理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：蛇绿岩对古板块运动具有指示作用,同时其赋存的铬铁矿等矿产是我国所短缺的矿产类型,所以蛇绿岩的研究具有重大的意义。纳木错西地处拉萨板块中部,班公湖-怒江缝合带与雅鲁藏布江缝合带之间的拉果错—嘉黎蛇绿混杂岩带东段;蛇绿岩分布错乱,岩块支离破碎,但岩石类型齐全,地幔橄榄岩类、堆晶杂岩类、镁铁质席状岩墙杂岩类、火山杂岩类及放射虫硅质岩等在研究区均有出露。研究区位置的蛇绿岩研究程度不高,且该区域蛇绿岩的形成环境及构造单元归属存在较大的争议;此外区内矿产多为新发现的矿床,研究其成矿作用对找矿前景具有重大意义。本文根据野外作业所得的资料与室内研究相结合,分析岩石组合、岩石地球化学等特征,从而对纳木错西蛇绿岩各组成单元及其形成的构造环境以及岩浆岩源区等进行深入讨论。结合在区域上构造演化的特征,对纳木错西地区的构造演化的研究提出新的地质依据及地质认识。此外,对研究区内与蛇绿岩建造有关的金属矿产,如铬铁矿、镍矿等,研究其矿产特征并对比他区蛇绿岩成矿作用,分析研究区蛇绿岩中矿产成因等。主要成果如下:(1)纳木错西蛇绿岩带岩石组合齐全,包括地幔橄榄岩、堆晶杂岩、席状岩墙群、枕状玄武岩四个单元,发现的伴生产物有条带状放射虫硅质岩及沉凝灰岩等。(2)研究区内蛇绿岩自底部到顶部其元素含量具有一个逐渐变化的过程;很好的解释了各单元的产生顺序。(3)综合前人研究数据和本次研究的玄武岩测年数据以及放射虫硅质岩中采获化石得出纳木错西蛇绿岩形成年代大致在晚侏罗世晚期的结论。(4)通过一系列岩石化学图解处理玄武岩的地学数据,了解到纳木错西蛇绿岩类似于消减带上的弧后盆地,通过洋中脊扩张作用产生。结合区域上发生的地质构造事件发现中生代时,中北冈底斯岩浆弧并不是一个统一的陆块,侏罗纪时,在其中北部一个伸展体制下形成了一个弧后盆地,并在早白垩世前消减闭合。(5)研究区中铬铁矿是当俯冲板块俯冲熔融的同时其中的水和CO_2逸散,形成热流进入地幔,导致地幔物质熔点降低,进而促进地幔橄榄岩的熔融,而一次或者数次熔融过程之后,导致铬富集,最终形成铬铁矿。(6)通过对比研究发现,研究区内玉古拉镍矿床的岩石学特征及岩石化学特征均与国内先前发现的几种镍矿床类型有较大的区别,可能为一种新的镍矿床成矿模式。
[Abstract]:The ophiolite could indicate the paleo plate movement, and the occurrence of chromite mineral resources in China are the shortage of mineral types, so the study of ophiolite is of great significance. The Nam Co is located in the Central West Lhasa plate, the Bangong Lake Nu River suture zone and the Yarlung Zangbo Suture Zone between Lagkor co - Jiali OPHIOLITIC MELANGE zone; ophiolite rock distribution disorder, but the rock types, reduced to fragments, mantle peridotite, cumulate complex rocks, mafic sheeted dyke complex, volcano complex rocks and radiolarian siliceous rocks in the study area were exposed. The location of the study area of ophiolite research degree high, and the area of the ophiolite controversial environment and tectonic units belong; in addition in mineral for new deposits, the mineralization is of great significance to prospecting. Based on the field work of the The data and laboratory research combined with analysis of rock composition, geochemical characteristics, and in-depth discussion on tectonic environment of each unit of ophiolite and the formation of the West Nam Co and magmatite source area. Combining the characteristics of the tectonic evolution in the region, put forward the understanding of geological basis and new geological structure of West Nam Co the evolution of the area. In addition, the study area and the ophiolite formation about metal mineral, such as chromite, nickel ore, study its mineral characteristics and contrast the ophiolite metallogenic analysis, mineral genesis of ophiolite. The main results are as follows: (1) west of Nam Co ophiolite rock combination complete, including the mantle peridotite cumulate complex, sheeted dike swarm, Pillow Basalt four units, found a byproduct of banded radiolarian siliceous rock and tuff. (2) in the study area from ophiolite The bottom to the top of the element content is a process of gradual change; a good explanation of the order of each unit. (3) the previous research data and the study of the Xuan Wuyan dating data and radiolarian siliceous rocks has been collected in the fossil that Nam Co West ophiolite formed in Late Jurassic generation roughly conclusion. (4) data through a series of rock chemical graphic processing Xuan Wuyan, learned that Nam Co West ophiolite is similar to the subduction zone of the back arc basin, produced by the effect of ocean ridge spreading. Combining with the geological structure that happened on the part that regional Mesozoic, North Gangdise magmatic arc is not a unified Jurassic continental block, in which a northern extension system formed a back arc basin, and cut closed in the early Cretaceous. (5) chromite in the study area is when the subducting plate subduction and its melting The water and the emission of CO_2, the formation of heat flow into the mantle, the mantle material leads to low melting point, and then promote the partial melting of mantle peridotite and one or several times after the melting process, resulting in chromium enrichment, and ultimately the formation of chromite. (6) it is found that both the petrological characteristics and chemical characteristics of rocks in the research area of jade goulas there is great difference between the nickel deposit and several nickel deposit types previously found at home, may be a new nickel deposit metallogenic model.

【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P611;P588

【参考文献】