【作者】 孙仁奇；

【导师】 裴先治；

【作者基本信息】 长安大学 ， 矿物学、岩石学、矿床学， 2007， 硕士

【摘要】 本文以岩石学、地球化学和同位素年代学研究为主,结合区域地质学、构造地质学、岩石大地构造学等方面的分析对祁连造山带东段葫芦河变质基性火山岩进行系统研究,确定其形成时代,识别其成因和大地构造环境,探讨火山岩在区域上的归属,进而阐明研究区的古板块构造演化历史,同时为探讨祁连造山带东段的组成、构造格架及形成演化乃至中国大陆造山带的基本特征及大陆动力学探索提供重要基础科学资料。通过对葫芦河变质基性火山岩的研究,获得主要结论和认识概括如下:(1)葫芦河变质基性火山岩以灰绿色变质玄武岩、玄武安山岩为主夹少量灰白色—浅灰色硅质岩。常量、稀土和微量元素地球化学特征及构造环境判别显示其总体上属于弧后盆地低钾拉斑玄武岩系列—钙碱性玄武岩系列过渡的岩石类型,兼具洋脊玄武岩和板内玄武岩的特征。微量元素特征表明其岩浆来源于受俯冲流体交代的富集地幔楔,并受到陆壳物质的混染。(2)利用锆石阴极发光图像(CL)和LA-ICP-MS锆石U-Pb定年方法,获得同位素测年结果为(436.9±5.7)Ma～(443.4±1.7)Ma,确定葫芦河变基性火山岩的形成时代为晚奥陶世。(3)祁连造山带东段地区于晚奥陶世伸展拉张,洋盆被打开,形成了陈家河群火山—沉积岩系;洋盆继续开裂,形成了晚奥陶世具有裂陷—小洋盆性质的葫芦河变基性火山岩带。(4)通过与红土堡变基性火山岩的对比研究认为,葫芦河变基性火山岩系与红土堡变基性火山岩系之间具有连接延伸关系,同属一个火山岩带。(5)研究区所在的祁连构造带与北秦岭构造带在早古生代时的交接关系是:北秦岭向西延伸变化为由微地块分割成多个有限洋盆和小洋盆系统,在早古生代洋盆打开并发育有不同类型蛇绿岩或裂谷火山岩等,进而形成多个火山岩浆岛弧构造带直至志留纪俯冲碰撞造山。早古生代杨家寺—红土堡—凤阁岭弧后裂陷小洋盆和胡毛—新城中酸性火山岛弧带是其中之一。更多还原

【Abstract】 This dissertation mainly studies Huluhe metabasic volcanic rocks in eastern section of Qilian orogenic belt primarily in petrography, geochemistry and isotopic geochronology combining with regional geology, structure, tectonics, etc., to define their ages, identify the cause of formation and tectonic settings, and to discuss their regional adscription. Further it illustrates the evolving history of paleo-plate in the study area; Meanwhile, it also provides important basic scientific data for discussing the composition , tectonic framework , forming and evolvement of eastern section of Qilian orogenic belt and the basic characteristics of continental orogenic belts, and exploring the continental dynamics in China.The following chief conclution and knowledge have been obtained by the studies of Huluhe metabasic volcanic rocks:(1) The Huluhe metabasic volcanic rocks are mainly composed of grayish green metabasalt and basaltic andesite, intercalated by a few offwhite-light-grey sillcalite. Geochemical characteristics of major elements, rare earth elements and trace elements , and the tectonic settings discrimination show that the metabasic volcanic rocks generally belong to back-arc basin tholeiitic basalt series- calc - alkalic basalt series with low kalium, also have the characteristics of MORB and WPB. Trace element characteristics show that the basic magma roots in enriched mantle wedge metasomatized by fluid in subduction belt, hybridized by continental crust material.(2) Using the cathodoluminescence (CL) images of zircons and LA-ICP-MS zircon U-Pb dating obtain the isotopic ages between (436.9±5.7)Ma and (443.4±1.7)Ma, which suggests that the Huluhe metabasic volcanic rocks formed in Late Ordovician.(3) Eastern section of Qilian orogenic belts extended in Late Ordovician Period , oceanic basin systems went through opening and formed Chenjiahe Group volcanic-sedimentary rock series; those oceanic basin systems went on opening and formed Huluhe metabasic volcanic rocks belt of back-arc rift-small ocean basin tectonic environment in Late Ordovician Period.(4) The comparative studies between Huluhe metabasic volcanic rocks and Hongtubao metabasic volcanic rocks show that there are conjunction and extension relation between them; they are of the same volcanic rocks belt.(5) The joining relation of Qilian and Northern Qinling tectonic belts in early Palaeozoic is that Northern Qinling extended westward to become many limited oceanic basin and small oceanic basin systems divided into by microlandmasses. These oceanic basin systems went through opening and developing various ophiolite or rift volcanic rocks etc.; Successively, many volcanic magma island arc tectonic belts formed, untill subduction, collision and orogenesis in early Palaeozoic. Early Palaeozoic Yangjiasi-Hongtubao-Fenggeling back-arc rift-small ocean basin and Humao-Xincheng intermediate-acidic volcanic island arc belts are one of the volcanic magma island arc tectonic belts.更多还原