西藏措美地区早白垩世岩浆岩地质年代学、地球化学及地质意义

发布时间：2018-03-01 11:11

本文关键词： 藏南双峰式火山岩超镁铁质岩基性脉岩 SHRIMP锆石定年地球化学　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：藏南隆子地区桑秀组中发育一套以英安岩和粗玄岩为主的双峰式火山岩组合,英安岩的SHRIMP锆石U-Pb年龄为134.9±2.3Ma,成岩时代为早白垩世。地球化学证据表明,粗玄岩富Ti O2、TFe O和P2O5,无明显HFSE亏损,英安岩Th、Nb、Zr、Y含量较高,而相对亏损P和Ti,Eu的负异常明显。粗玄岩可能是Kerguelen地幔柱与岩石圈地幔相互作用的产物,而英安岩的形成与地壳深熔作用有关。藏南地区广泛发育近东西向的基性岩墙群,其中哲古地区辉石岩以夹层形式产于辉长岩中,对哲古基性岩进行SHRIMP锆石U-Pb定年,得出辉长岩和辉石岩加权平均年龄分别为131.71±2.7Ma(2σ,MSDW=2.8)和135.0±2.4Ma(2σ,MSDW=2.1),辉石岩的结晶时代早于辉长岩约4Ma。元素地球化学研究表明,辉长岩Si O2含量为50.85%,Ti O2含量为1.45%,Mg O含量为10.05%,全铁含量为8.57%,镁数为71.33。辉石岩Si O2含量为48.28%,Ti O2含量为2.02%,Mg O含量为18.68%,全铁含量为13.08%,镁数为78.76。辉长岩和辉石岩K2O含量较高,分别为0.68和0.81,Eu的亏损不明显,相对亏损Nb、Ta等元素,稀土分布型式与板内洋岛玄武岩(OIB)类似。其形成与同时期的地幔热事件关系密切,并在上升过程中可能受到了地壳物质的混染。藏南隆子-古堆一带广泛发育近东西走向的基性脉岩尚未得到很好的约束,对基性脉岩做了较为系统的地质年代学和岩石地球化学研究,3个基性脉岩的SHRIMP锆石U-Pb年龄为133-140.9Ma,代表了辉长岩的结晶年龄,元素地球化学研究表明,基性脉岩属于钙碱性-碱性系列,总体富Ti O2,平均含量为3.08,LREE富集,轻重稀土分异较为明显,LILE略为富集,HFSE亏损不明显,属被动大陆边缘构造环境。
[Abstract]:A set of bimodal volcanic assemblages consisting mainly of dolomite and trachyte are developed in the Sangxiu formation of southern Tibet. The SHRIMP zircon U-Pb age of the dolomite is 134.9 卤2.3 Ma.The diagenetic age is early Cretaceous. Geochemical evidence shows that, The coarse rocks are rich in TIO _ 2, TFE _ O and P _ 2O _ 5, and have no obvious HFSE depletion. The contents of Thnbszru _ Y are relatively high, while the relative depletion of P and Ti-EU are obvious. The coarse rocks may be the product of interaction between Kerguelen mantle plume and lithospheric mantle. The formation of dolomite is related to deep crustal melting. In southern Tibet, there are widely developed near-east-west basic-dike groups, in which pyroxenite occurs in gabbro in the form of intercalation, and the SHRIMP zircon U-Pb dating is carried out for the geostrophic rocks. The weighted mean ages of gabbro and pyroxenite are 131.71 卤2.7 Ma ~ (2 蟽) and 135.0 卤2.4 Ma ~ (2 蟽) respectively. The crystallization age of pyroxenite is earlier than that of gabbro about 4 Ma.Elemental geochemistry study shows that. The content of Sio _ 2 in gabbro is 50.85, the content of TIO _ 2 is 1.45 and the content of MgO is 10.05, the content of total iron is 8.57, the amount of magnesium is 71.33. The content of Sio _ 2 in pyroxenite is 48.28, and the content of TIO _ 2 is 2.02mg _ O, the content of total iron is 13.08, the content of magnesium is 78.76. The content of K _ 2O in gabbro and pyroxenite is higher. The depletion of 0.68 and 0.81 EU is not obvious, and the REE distribution pattern is similar to that of OIBB, and the REE distribution pattern is closely related to the mantle thermal events in the same period. During the process of uplift, it may be contaminated by crustal materials. The basic dike rocks, which are widely developed in the area of Longzi to Gudui in the south of Tibet, have not been well constrained by the east-west trend. The geochronology and geochemistry of the basic dikes have been systematically studied. The SHRIMP zircon U-Pb ages of the three basic dikes are 133-140.9 Ma, which represent the crystallization age of gabbro. The basic dike rocks belong to the calc-alkaline alkaline series, which are rich in TIO _ 2, and the average content is 3.08% LREE, and the difference between light and heavy rare earth elements is relatively obvious. The Lile is slightly enriched and the loss of HFSE is not obvious. It belongs to the passive continental margin tectonic environment.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.1;P597.3

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