日喀则蛇绿岩与IBM前弧中部蛇纹岩的地球化学特征及构造环境研究

发布时间：2018-04-17 03:12

本文选题：蛇绿岩 + 微量元素　；参考：《青岛科技大学》2015年硕士论文

【摘要】：蛇绿岩的概念从提出到形成经历了很漫长的过程,最终形成了现在人们普遍认可的概念。蛇绿岩并不是一类岩石或矿物,而是一系列有序排列的岩石的组合,又称为蛇绿岩套。一个发育完整的蛇绿岩从下到上的岩石序列分别为：超镁铁质杂岩、辉长质杂岩、席状岩墙、镁铁质火山杂岩、海底沉积岩等。并不是所有的蛇绿岩都具有上述完整的序列,也并不是只要发现这样的组合序列就一定是一整套蛇绿岩,有些只是不相关的岩石随机组合在一起,这就需要通过年代学、地球化学和岩石学是否具有亲缘性来验证。从全球构造来看蛇绿岩基本上可以分为两大类：(1)与俯冲相关的蛇绿岩,主要包括超俯冲地带(SSZ)和火山弧类型。(2)与俯冲不相关的蛇绿岩,主要包括大陆边缘型、洋中脊型和地幔羽型。本文所研究的样品都属于第一种类型。本文通过矿物学及岩石学、地球化学、U-Pb测年对西藏日喀则地区蛇绿岩与IBM岛弧中部蛇纹岩进行了详细的研究。通过这些研究发现,日喀则地区所采集的样品中橄榄岩、玄武岩和硅质岩有可能属于同一蛇绿岩,白朗地区的滑石化辉石是由陆壳生成的,不属于蛇绿岩。橄榄岩的REE图显示其产生于SSZ环境,硅质岩的地球化学特征显示其为生物成因非热液成因。IBM岛弧中部的橄榄岩几乎全部发生了蛇纹石化,将IBM岛弧中部蛇纹石化橄榄岩与IBM岛弧南部蛇纹石化橄榄岩、ODP钻井得到的橄榄岩进行对比,发现不仅海水对橄榄岩的蛇纹石化影响严重,俯冲速度、海底地形等也对其有一定的影响,这需要做进一步的研究。将日喀则地区的橄榄岩与IBM岛弧中部的蛇纹岩进行比较,发现两者的微量元素及REE图的变化趋势相似,但是前者的原岩成分比后者更加亏损,推测两者具有同源性。
[Abstract]:The concept of ophiolite has gone through a long process from putting forward to forming.Ophiolite is not a kind of rock or mineral, but a series of orderly rock assemblage, also known as ophiolite suite.A complete sequence of ophiolite rocks from the bottom to the top are: ultramafic complex, pyroxenite complex, schist dike, mafic volcanic complex, submarine sedimentary rock and so on.Not all ophiolite have these complete sequences, nor do they have to be a whole set of ophiolite once they are discovered, some of which are just random combinations of unrelated rocks, which need to be chronologically studied.Geochemistry and petrology are related to verify.According to the global structure, ophiolite can be basically divided into two categories: 1) subduction-related ophiolite, mainly including the supersubduction zone (SSZ) and volcanic arc type. (2) subducted ophiolite, mainly including continental margin type.Mid-ocean ridge and mantle plume.The samples studied in this paper belong to the first type.By means of mineralogy, petrology and geochemistry U-Pb dating, the ophiolite in Xigaze area, Tibet, and the ophiolite in the middle of IBM island arc are studied in detail in this paper.Through these studies, it is found that peridotite, basalt and silicalite may belong to the same ophiolite in the samples collected in Xigaze area, and the talcitabyte in Bai Lang area is formed from continental crust, not ophiolite.The REE diagram of peridotite shows that it originated in SSZ environment, and the geochemical characteristics of siliceous rock indicate that it is biogenic non-hydrothermal origin. Almost all peridotite in the middle of IBM-arc occurred serpentine.By comparing the serpentine peridotite from the central part of the IBM island arc with the peridotite drilling from the southern part of the IBM island arc, it is found that not only sea water has a serious influence on the serpentine fossilization of the peridotite, but also the subduction velocity.The submarine topography also has some influence on it, which needs further study.By comparing the peridotite in Xigaze area with the ophiolite in the middle of IBM Island Arc, it is found that the trace elements and REE map of the two are similar, but the original rock composition of the former is more depleted than that of the latter.
【学位授予单位】：青岛科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.323

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