广西浦北花岗岩岩石学及地球化学研究

发布时间：2018-01-26 00:23

本文关键词： 浦北花岗岩花岗岩体包体地球化学特征岩石成因　出处：《成都理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：本文以大容山花岗岩(南)东亚带中的浦北岩体为研究对象,通过对花岗岩、包体及地球化学特征三个方面的详细研究,分析了花岗岩的特征、包体的特征及与寄主花岗岩的相互关系、花岗岩地球化学特征,并探讨了岩石成因类型。浦北花岗岩位于大容山花岗岩(南)东亚带,岩体主要由黑云母花岗岩构成,根据结构可分为中心相、过渡相和边缘相带。中心相带由中粗粒花岗岩组成;过渡相带由细中粒花岗岩组成;边缘相带有细粒或中细粒花岗岩组成,其中以过渡相较发育,各岩相之间均为过渡关系。基质的形成温度明显的低于斑晶,说明虽然岩石具有似斑状结构,但斑晶和基质并非同时形成,斑晶形成较早,基质是在岩浆进一步冷却结晶过程中所形成的。浦北花岗岩中所含包体均为变质岩包体,矿物组合为石英+斜长石+钾长石+黑云母±堇青石±石榴石±矽线石,属于角闪岩相。形成温度为中温,最高500℃,低于寄主花岗岩的形成温度,表明包体是先形成的,花岗岩是变质岩重熔形成的。包体具有富铝质特征,变质岩包体的原岩为泥质岩。浦北花岗岩中Si O2含量高,为钙碱性岩,属高钾钙碱性系列。岩石中铝饱和指数ASI1.1,岩石表现出铝过饱和,属于过铝质花岗岩。K相对富集,Na含量较低,Na2O/K2O1。K2O-Na2O图解中投射区落在S型花岗岩范围内。浦北花岗岩为壳源花岗岩,其形成岩浆由上部陆壳物质熔融产生。花岗岩中稀土元素特征与上部陆壳的稀土元素特征相似,稀土总量均较大,LREE较HREE分异程度好。稀土元素分配模式图中曲线均呈右倾,LREE曲线呈中等斜率,HREE曲线近于平缓,具有明显的负Eu异常。浦北花岗岩中Rb、Th、La、U相对富集,而Ba、Nb、Sr亏损,与S型花岗岩微量元素分配模式相似。根据浦北花岗岩岩石学及地球化学的特征,与I型、S型花岗岩对比后确定浦北花岗岩属于S型花岗岩。浦北花岗岩的形成与钦防残留洋盆的关闭密切相关,它形成于钦防残留洋盆向南俯冲碰撞过程中的岛弧背景。
[Abstract]:Based on the study of the Pubei rock body in the Darongshan granite (south) East Asian belt, this paper analyzes the characteristics of the granite in detail from three aspects: granite, inclusion and geochemistry. The characteristics of the xenoliths and their relationship with host granites, the geochemical characteristics of the granites, and the petrogenetic types of the granites are discussed. The Pubei granites are located in the Darongshan granite (south) East Asian belt. The rock mass is mainly composed of biotite granites, which can be divided into central facies, transitional facies and marginal facies belt according to the structure. The central facies belt is composed of medium-coarse granites. The transitional facies zone is composed of fine-grained granites; The marginal facies are composed of fine-grained or medium-fine-grained granites, in which the transitional facies is relatively developed, and the transition relationship is between each lithofacies. The formation temperature of the matrix is obviously lower than that of the porphyry, which indicates that the rocks have a porphyry like structure. However, the porphyry and matrix did not form at the same time, and the porphyry formed earlier, and the matrix was formed during the further cooling and crystallization of magma. The inclusions contained in Pubei granite are metamorphic inclusions. The mineral assemblage is quartz plagioclase potassium feldspar biotite 卤cordierite 卤garnet 卤sillimanite, which belongs to amphibolite facies. The results show that the inclusions are formed first and the granites are formed by the remelting of metamorphic rocks. The xenoliths are aluminum-rich, and the primary rocks of the xenoliths are argillaceous rocks. In Pubei granite, the content of Sio _ 2 is high, which is calc-alkaline. It belongs to the high-potassium calc-alkaline series. The aluminum saturation index (ASI1.1) in the rocks shows aluminum supersaturation, which belongs to the peraluminous granite. K is relatively rich in Na content. The projection area in the Na2O/K2O1.K2O-Na2O diagram falls within the range of S-type granite. Pubei granite is a crust-derived granite. The magma is formed by the melting of the upper continental crust. The characteristics of rare earth elements in the granite are similar to those in the upper continental crust, and the total amount of rare earth elements is large. LREE is better than HREE. The curve of REE distribution pattern is right tilted and LREE curve is medium slope and hree curve is close to flat. There is an obvious negative EU anomaly in Pubei granite, where the RbPU is relatively enriched and the Ba-NbPU Sr is depleted. The distribution pattern of trace elements is similar to that of S-type granite. According to the petrological and geochemical characteristics of Pubei granite, it is similar to that of type I. Compared with S-type granite, Pubei granite belongs to S-type granite. The formation of Pubei granite is closely related to the closure of Qinphang residual ocean basin. It was formed in the island arc background during the southward subduction and collision of the residual ocean basin.
【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】：P588.121

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