巴基斯坦信德地区纳格尔巴格尔杂岩学元素地球化学特征与锆石U-Pb年龄

发布时间：2018-01-11 01:17

本文关键词：巴基斯坦信德地区纳格尔巴格尔杂岩学元素地球化学特征与锆石U-Pb年龄　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：纳格尔巴格尔杂岩体位于巴基斯坦南部与印度交接的巴格尔沙漠地区,靠近信德省大卡奇沼泽地,由变质岩、侵入岩和火山岩组成,这些岩石以深成岩体的形式出露于沙漠平原中,其中花岗岩是主要岩石类型。本研究的主要目的是测定纳格尔巴格尔杂岩体岩石的年龄和元素组成,以期对其成因、演化过程和大地构造背景进行制约。为此,本文对采自纳格尔巴格尔地区9个侵入体的28块代表性岩石样品进行了详细的锆石235U-207Pb年龄分析和主量元素及微量元素测定。为获得U-Pb年龄数据,岩石样品被机械破碎以筛选出锆石晶体,随后这些锆石被固定在环氧树脂靶上并抛光。表面喷碳后,这些锆石靶用装配于Tescan扫描电子显微镜上的Gatan Chroma CL阴极光谱仪获得锆石的CL图像,测定235U-207pb年龄的目标点被标注于锆石的CL图像上。235U-207Pb年龄采用LA-ICP-MS进行分析,在中国科学技术大学-中科院壳幔物质导环境重点实验室完成。235U-207Pb年龄测定结果在经过普通铅校正后由计算机软件得到其谐和年龄图解与加权平均年龄图解。所有样品的全岩主微量元素组成使用XRF、ICP-MS和ICP-AES在广州澳实实验室测定。结果在构造环境判别图解中投点以区别各岩石的分类、对应的构造环境关系以及物质来源。岩石微量元素组成在球粒陨石和原始地幔标准化图解中的富集和亏损异常被用来推断岩浆的原始源区。结果表明,杂岩体中深成岩是大陆下地壳部分熔融的产物,这些岩浆受到前存大陆下地壳围岩的同化混染。卡奇地区随后因纳格尔巴格尔断裂的再次活跃和拉贾斯坦与卡奇附近地区的相关裂谷活动而被抬升。该地区具有富集地幔来源特征的火山岩证明该区域在抬升后又经历了火山活动。根据出露岩石的地球化学组成判断,本区域在构造环境判别图解被归为板内花岗岩成因环境,杂岩体花岗岩具有中等到高的钾-钙含量特征,是典型的A型花岗岩。样品的锆石235U-207Pb年龄结果表明有三期主要的岩浆活动存在:(a)变质作用阶段:片麻岩具有884±6Ma的变质年龄,角闪岩具有818±7 Ma的变质年龄;(b)深成作用阶段:深成岩浆活动从815 Ma持续到730 Ma,期间发生数次间断性活动,产生了长英质、中性和镁铁质岩浆;(c)火山活动阶段:形成283.2±2 Ma的粗面岩。结合地球化学特征来看,纳格尔巴格尔杂岩体形成于冈瓦纳大陆裂谷扩张阶段,具有两种不同的物质来源,并且与印度地盾的拉贾斯坦克拉通地区在后德里岩浆事件中的马拉尼火成岩套在地域上具有关联性。
[Abstract]:The Nagar Bagger complex is located in the Bagger desert area, near the Grand Kachi Everglades in Sindh Province. It is composed of metamorphic rocks, intrusive rocks and volcanic rocks. These rocks are exposed to desert plains in the form of deep rock masses, among which granite is the main rock type. The main purpose of this study is to determine the age and elemental composition of the rocks in the Nagel Bagger complex. In order to restrict its origin, evolution process and tectonic background. In this paper, 28 representative rock samples collected from 9 intrusions in the Nagel Bagger area were analyzed in detail for zircon 235U-207Pb age and determination of principal elements and trace elements. B Age data. Rock samples are mechanically broken to screen out zircon crystals, which are then fixed on epoxy targets and polished. The surface is sprayed with carbon. The CL images of zircon were obtained by Gatan Chroma CL cathodic spectrometer assembled on Tescan scanning electron microscope. The target point for the determination of 235U-207pb age was labeled on the CL image of zircon. The age of 235U-207Pb was analyzed by LA-ICP-MS. The results of age determination of .235U-207Pb in the key laboratory of crust-mantle material conduction environment of the University of Science and Technology of China and the Chinese Academy of Sciences have been obtained by computer software after the correction of common lead. Weighted mean age diagram. All samples of the main and trace elements of the whole rock composition using XRF. ICP-MS and ICP-AES were measured in Guangzhou Australian laboratory. Results the input points were used to distinguish the classification of rocks in the tectonic environment discriminant diagram. The enrichment and depletion anomalies of trace element composition in chondrites and primitive mantle are used to infer the original source of magma. The deep diagenetic rock in the complex is the product of partial melting of the lower continental crust. The magma was assimilated by the surrounding rocks of the lower crust of the pre-existing continent. The Karch area was subsequently uplifted by the reactivation of the Nagel Bagger fault and the associated rift activities in the vicinity of Rajasthan and Kachi. The volcanic rocks enriched in mantle origin show that the region experienced volcanic activity after uplift. The geochemical composition of exposed rocks is judged. In this area, the tectonic environment discriminant diagram is classified as the genetic environment of intraplate granite, and the complex granite has the characteristics of medium to high potassium and calcium content. The zircon 235U-207Pb age of the sample indicates that there are three major magmatic activities in the three stages. Metamorphic stage: gneiss has a metamorphic age of 884 卤6 Ma. Amphibolite has a metamorphic age of 818 卤7 Ma. (B) the deep magmatic activity lasted from 815 Ma to 730 Ma, during which several intermittent activities occurred, resulting in felsic, neutral and magnesite magma; (C) volcanic activity stage: the coarse rock formed at 283.2 卤2 Ma. In combination with geochemical characteristics, the Nagel Bagger complex was formed in the Gondwana continental rift extension stage. There are two different sources of material, and they are geographically related to the Malani igneous rocks in the Rajasthan craton of the Indian Shield in the post-Delhi magma event.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P597.3;P584

【相似文献】