西南天山高压超高压岩体的分类及地球化学特征

发布时间：2018-03-10 05:09

本文选题：西南天山　切入点：榴辉岩　出处：《西北大学》2015年硕士论文　论文类型：学位论文

【摘要】：自1997年发现榴辉岩后,西南天山高压-超高压变质带受到国内外学者的广泛关注和研究。该变质带主要由榴辉岩、蓝片岩以及云母片岩构成,并与北部以片麻岩和斜长角闪岩为主的低压高温带构成双变质带。西南天山的榴辉岩依据产状分为五种类型：云母片岩中的薄层状和透镜状榴辉岩、与蓝片岩互层的榴辉岩薄层、枕状构造榴辉岩／蓝片岩、大理岩中的榴辉岩和大型榴辉岩体。西南天山超高压变质作用为4个变质阶段：1.硬柱石-蓝片岩阶段；2.绿帘石-榴辉岩阶段；3.绿帘石-蓝片岩阶段；4.绿片岩相阶段。地球化学分析结果显示：西南天山的蓝片岩、蓝闪石岩岩枕和榴辉岩的原岩主体为拉斑玄武岩和碱性玄武岩。从N-MORB标准化的稀土配分模式中得出蓝片岩和蓝闪石岩岩枕的原岩介于介于E-MORB和OIB之间；榴辉岩原岩有两种类型：第一类是E-MORB型,且有Ba、U富集的特点；第二类是OIB型。蓝片岩、蓝闪石岩和榴辉岩的构造环境为近洋岛环境。样品ATT-75蓝片岩中粒径较大的绿帘石族矿物有清晰的环带,并伴有放射状裂纹。通过电子探针分析该类矿物主要为绿帘石,少部分为斜黝帘石矿物。放射状裂纹及环带表明其形成为三期,第一期的核部形成于深俯冲时期,第二期幔部及第三期边部形成于折返阶段。在折返后,由于压力降低,核部体积增大造成放射状裂纹。样品中的绿帘石矿物的核部-幔部-边部的XFe3+成分变化复杂,核部-边部的总体趋势为退变质。
[Abstract]:Since the discovery of eclogite in 1997, the high-ultrahigh pressure metamorphic belt in the southwest Tianshan Mountains has attracted extensive attention and research from domestic and foreign scholars. The metamorphic zone is mainly composed of eclogite, blueschist and mica schist. The eclogite in southwest Tianshan is divided into five types according to its occurrence: thin layer eclogite and lenticular eclogite in mica schist. Eclogite thin layer interbedded with blue schist, occipital eclogite / blue schist, Eclogite and large eclogite in marble. The ultrahigh pressure metamorphism of southwest Tianshan is divided into four metamorphic stages: 1: 1. The hard columnite-blue schist stage 2. The green curtain-eclogite stage 3. The green curtain-blue schist stage 4. The greenschist facies order. Geochemical analysis shows that the blueschist in the southwest Tianshan Mountains, Tholeiite and alkaline basalt are the main bodies of the blueschist pillow and eclogite. From the N-MORB standardized REE distribution model, it is found that the protolith of the blueschist and blublenite pillow is somewhere between E-MORB and OIB. There are two types of eclogite protolites: the first type is E-MORB type, and the second type is OIB type. The tectonic environment of blue diorite and eclogite is near oceanic island environment. There is a clear ring zone and radial crack in the larger diorite group minerals in the ATT-75 blueschist. The radial cracks and the annular zone indicate that the first stage formed in the deep subduction period, the second stage in the mantle and the third stage in the exhumation stage. The change of XFe3 composition in the core mantle edge of the sample is complex and the general trend of the nucleus-edge part is retrograde metamorphism.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.3

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