四川省越西地区峨眉山玄武岩地质及地球化学特征研究

发布时间：2018-04-25 20:34

本文选题：峨眉山玄武岩 + 地质特征　；参考：《成都理工大学》2016年硕士论文

【摘要】：分布在云、贵、川3省的二叠纪至三叠纪的玄武岩,一直备受众多学者关注。峨眉山大火成岩省总体分布在扬子地块西缘,目前来说它是我国为数不多被国际地学界认可的大火成岩省。而在我国矿产分布方面,峨眉大火成岩省是西南地区典型的集矿区域。由于其成因主要与地幔柱活动有关,所以它显著特点为产出大量火山岩浆岩系的时间很短。由此看出峨眉山玄武岩的研究对我们探讨地幔柱演化、形成及其地质效应都有指示意义,峨眉大火成岩省便成为开展地幔柱研究非常理想的地区。通过野外实测剖面分析发现区内峨眉山玄武岩组厚度约为1571.25m。与上覆须家河组地层呈平行不整合接触,与下伏阳新组为喷发不整合接触关系。结合野外观察和前人的资料将其分为三段。越西峨眉山玄武岩组是以溢流相为主,爆发相次之。论文通过对越西地区峨眉山玄武岩镜下岩相学研究、岩石地球化学实验分析,通过实验数据界定主量元素的含量变化范围。对数据进行细致分析,同时对超出合理范围的样品进行相应解释。通过哈克图解、TAS图解、硅-钾图等分析主量元素性质。稀土元素分馏情况灵敏地反映出岩石的成因和源区特征。越西地区峨眉山玄武岩稀土配分模式图呈明显的右倾型,而大陆碱性玄武岩是富集轻稀土的右倾斜线。微量元素中大离子亲石元素K、Sr、Ba强烈亏损,而Rb、LREE相对富集。同时高场强元素Nb、P、Ce强烈亏损,Th、Zr、HREE相对富集。但是大离子亲石元素中K、Sr、Ba及重稀土元素中的Yb波动范围较大,相应样品结合镜下观察分析基本排除了蚀变的可能,所以初步判断应该是岩浆的同化混染作用造成的。在岩浆源区方面,分析结果表明越西峨眉山玄武岩来源于高压高熔融的条件下的石榴石相,结晶温度较高,随着深度的变化,压力降低,温度降低,熔融程度减小,形成了玄武岩。同时初步判定越西地区峨眉山玄武岩是源自地幔柱不是岩石圈地幔。
[Abstract]:The Permian to Triassic basalt distributed in Yunnan, Guizhou and Sichuan provinces has been concerned by many scholars. Emeishan great igneous province is distributed in the western margin of Yangtze block and is one of the few major igneous provinces recognized by the international geosciences in China. In the distribution of mineral resources in China, Emei great igneous province is a typical ore gathering area in southwest China. Because its genesis is mainly related to mantle plume activity, it is characterized by a short time to produce a large number of volcanic magmatic rocks. It can be seen that the study of Emeishan basalt is instructive for us to study the evolution of mantle plume and its formation and geological effects. Emei igneous province is an ideal region for the study of mantle plume. It is found that the thickness of Emeishan basalt formation is about 1571.25m. There is a parallel unconformable contact with the Xujiahe formation and an eruption unconformity with the Xiafuyangxin formation. Combined with field observation and previous data, it is divided into three sections. The Emeishan basalt formation in Yuexi is dominated by overflow facies, followed by explosive phase. In this paper, the lithofacies of Emeishan basalt in Yuexi area is studied under the microscope, and the range of main elements content is defined by the experimental data. Analyze the data carefully and interpret the samples beyond the reasonable range. The properties of principal elements were analyzed by means of Huck diagram, TAS diagram and Si-K diagram. The fractionation of rare earth elements sensitively reflects the origin and source characteristics of rocks. The REE distribution pattern of Emeishan basalt in Yuexi area shows an obvious right-dip pattern, while continental alkaline basalt is the right-dip inclined line for the enrichment of LREE. The large ion lithophile element K ~ (2 +) Sr ~ (2 +) Ba in trace elements is strongly depleted, while the RbBX LREE is relatively enriched. At the same time, the high field strength element NbPX ce is strongly depleted and the HREE is relatively enriched. However, the fluctuation range of K ~ (2 +) Sr ~ (2 +) Ba in large ion lithophile elements and Yb in heavy rare earth elements is large, and the possibility of alteration is basically excluded from the corresponding sample observation and analysis under microscope, so the preliminary judgement should be caused by the assimilation and contamination of magma. In the magmatic source area, the results show that the basalts of Emei Mountain in Yuexi are derived from the garnet phase under high pressure and high melting, and the crystallization temperature is higher. With the change of depth, the pressure decreases, the temperature decreases and the melting degree decreases. Basalt was formed. At the same time, it is preliminarily determined that the Emeishan basalt originates from mantle plume and not lithospheric mantle in Yuexi area.
【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】：P588.145

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