北京房山花岗闪长岩体中包体的演化及闪长质微粒包体的成因  

Evolution of Enclaves in Beijing Fangshan Granodiorite and Genesis of Dioritic Microgranular Enclaves

作　　者：陶继东[1] 马昌前[2] 张金阳[3] 王书纯[4] 王人镜[2] 

机构地区：[1]中国地质大学研究生院,武汉430074 [2]中国地质大学地球科学学院,武汉430074 [3]中国地质大学资源学院,武汉430074 [4]中国地质大学信息中心,武汉430074

出　　处：《地质科技情报》2009年第2期33-41,共9页Geological Science and Technology Information

基　　金：教育部和国家外国专家局高等学校学科创新引智计划项目(B07039);国家自然科学基金委员会创新群体基金项目(40821061)

摘　　要：依据53个观察点2 615个包体的统计,将房山花岗闪长岩体中的包体划分为捕虏岩包体和微粒包体两大类。包体与岩体在组分上具有明显的浓度差,在物理化学上是不平衡的,包体与岩浆之间必然发生交互反应,从而形成包体的同心环带构造。捕虏岩包体环带构造特别发育,尤其是碳酸盐岩包体。根据50余个包体岩石薄片观察、矿物化学及岩石化学分析结果,将碳酸盐岩包体从早到晚的演化规律划分为4个阶段:热变质角岩化阶段→超镁铁质基性岩化阶段→中基性岩化阶段→中酸性岩化阶段,直至包体消失。56个微粒包体岩石薄片鉴定结果表明,其主要组成矿物是普通角闪石、黑云母和斜长石,组成和体积分数与闪长岩相当,因此又称为闪长质包体,定量统计结果表明,暗色闪长质包体的暗色矿物体积分数>35%,浅色闪长质包体的暗色矿物体积分数<35%,后者可构成前者的浅色边。根据闪长质微粒包体的宏观特征及分布规律、特殊的结构构造、主要造岩矿物与寄主岩的对比以及6 187个斜长石双晶类型百分率的成因分析得出,房山花岗闪长岩体中的闪长质微粒包体尽管有多种成因,但有不少可能是捕虏岩包体变质改造的结果。According to the statistics of 2615 enclaves in 53 enclave observation spots, enclaves in Fangshan granodiorite are divided into two categories, xenolith enclave and microgranular enclave. The concentric zonal structure of enclave was formed because of the obvious differential concentration of enclave and pluton components, physicochemical imbalance and interaction between enclave and magma. Xenolith enclave zonal structure developed much, especially for carbonate enclaves. According to the observation on more than 50 enclave rock slices and the results of mineral and rock chemical analysis, the evolution law of xenolith enclave is divided into four phases： phase of hornfels, phase of ultramafic basic rock, phase of intermediate-basic rock,and phase of intermediate-acid rock, then till disapearance of enclave. The identification of 56 microgranular enclave rock slices shows that, the main composite minerals are hornblende, biotite and plagioclase and that components and contents are equivalent with diorites, thus microgranular enclave is also called dioritic enclave. The quantitative statistics demonstrates that enclave with more than 35% dark minerals is called dark dioritic enclave, and enclave with less than 35% dark minerals is called light-colored dioritic enclave. Some of the latter consititues the light-colored edge of the former. According to the macro-characteristics and distribution law of dioritic microgranular enclaves, the special texture and,structure, the contrast between the main rock-forming minerals of dioritic microgranular enclave and the host rock, as well as the genesis analysis on double crystal type percentage of 6 187 plagioclase, the conclusion is drawn as follows： despite the variety of the genesis types of dioritic microgranular enclave in Fangshan granodiorite, most of the genesis type is probably the result of the xenolith metamorphic transformation.

关 键 词：房山花岗闪长岩体 微粒包体成因 捕虏体演化 

分 类 号：P585[天文地球—岩石学]