【作者】 李瑜；

【导师】 阳正熙；

【作者基本信息】 成都理工大学 ， 矿产普査与勘探， 2016， 硕士

【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CO₂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。更多还原

【Abstract】 Ophiolite have Indicative function to the plate movement and the chromite ores which consist in the ophiolite is the scarce mineral type to our country, so the study to the ophiolite have great significance. West Namcuo located in the central of Lhasa plate, east paragraph of Laguocuo-Jiali ophiolite belt which is situated between Bangongcuo-Nujiang suture and Yarlung zangbo River suture; the ophiolite in west Namcuo distributing in disorder, but it have complete rock type; the mantle peridotite class, the cumulate rocks class, the magnesium iron sheet diked swarm class, the volcano miscellaneous rock class, the radiolarian silicalite and so on expose in research district.The ophiolite in the study area is degree is scarce, it’s lithogenesis environment and structural unit belonging there is great controversy; also minerals in the area are newly discovered deposits, research the metallogeny of the ophiolite have great significance for prospecting.This article according to gathered information from field work and laboratory study, analysis of the group and geochemical characteristics and so on of the ophiolite in the area; then debate with every unit of the ophiolite in the west Namcuo, the lithogenesis environment and magmatic source area. Combining the feature of tectonic evolution in the area, Propose new geological basis and geological cognition of the tectonic evolution of the weste Namcuo area. In addition, study on the mineral characteristics in the metal ores which associated with ophiolites in the study area, such as chromite, nickel, and compare metallogeny of the ophiolite in other area, analyze the causes of ophiolites in the minerals in the study area. The main results are as follows:（1） The ophiolitic rocks in the west Namcuo, including four units as the mantle peridotite class, the cumulate rocks class, the magnesium iron sheet diked swarm class, the volcano miscellaneous rock class, the radiolarian silicalite and tuff Rock and so on as associated products.（2） Ophiolite of study area from the bottom to the top of its element content with a gradual process; explain the order of the Ophiolite very well.（3） Previous research data and the study of the basalt dating data collected fossils in the Radiolarian cherts then concluded that West Namco Ophiolite formed roughly at the late Jurassic.（4） Through a series graphic processing of geological data which from basalt rocks, understand the West Namcuo Ophiolite similar to the subduction zone on the back-arc basin, generated by the mid-ocean ridge dilatation. Associate regional geological event occurred found that Middle-North Gangdise magmatic arc was not unified in the Mesozoic, Middle-North Gangdise northern extension was formed a back-arc basin in Jurassic, and cut closed prior to Early Cretaceous.（5） The chromite in research district was generated by dive plate dive melting while water and CO₂ in the plate was lossn, formed heat flow into mantle, led to mantle material melting point reduced, then promote mantle olive rock of melting, and after once or number times melting process like this, led to chrome rich set, eventually formed chromite.（6） Through compared research found that petrology and petrochemistry characteristics of nickel deposit in research district have great different from previously found of several nickel deposit type in our country, maybe it is a new nickel deposit mine mode.更多还原