西藏夏瓦地区岩浆岩年代学、地球化学及地质意义

发布时间：2018-07-11 11:57

  本文选题：岩浆岩 + 锆石U-Pb年龄　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：近年来,许多学者对特提斯喜马拉雅带白垩纪火山岩非常关注。研究区位于特提斯喜马拉雅带中东部,古地理上属大印度北缘,也位于措美残余大火成岩省范围内。本论文拟通过对岩浆岩地球化学及年代学的研究,分析其成因、构造环境,为新特提斯洋扩张及措美大火成岩东延提供证据,也为进一步找矿指明方向。西藏夏瓦地区火山岩的岩石类型主要为英安岩、粗面玄武岩、安山质玄武岩。获得英安岩锆石U-Pb年龄为142±1.0Ma,其形成时代为早白垩世。元素地球化学研究表明,玄武岩是富Ti、Fe、P、Mg过铝质碱性玄武岩,与OIB特征相似;稀土元素总量∑REE=270.01-311.19ppm,LREE略富集,大离子亲石元素中相对富集Ba,贫K、Sr;在高场强元素中相对富集Th、U、Zr、Hf,贫Nb;Eu异常不明显。英安岩是富Si、Al、K、Ca,贫Mg、Fe的过铝质钙碱性酸性岩;稀土元素总量∑REE=266.20-555.8ppm,富集LREE,在大离子亲石元素中相对富集Rb、Ba,亏损Sr、K、Eu;在高场强元素相对富集Th、U,亏损Nb、Ti、Zr、Hf;具有明显Sr负异常,可能与低压条件下的斜长石分离结晶有关;Th丰度高(平均为40.1ppm),Nb/La平均为0.29,暗示与硅铝质地壳的深熔作用有关。西藏夏瓦地区基性脉岩的岩石类型主要为辉长岩、辉绿岩,近东西向展布。获得2个辉长岩锆石U-Pb年龄分别为145.99±0.98Ma和146.12±0.72Ma,其结晶时代均为早白垩世。元素地球化学研究表明,辉长岩、辉绿岩富集全碱、Ti、Fe、P、Mg,属钙碱性系列,与OIB特征相似;稀土元素总量ΣREE=897-1121ppm,LREE略富集,在大离子亲石元素中相对富集Ba、亏损K、Pb、Sr;在高场强元素中相对富集Nb、Ta、Zr、Hf、Th,亏损U、Ti;Eu弱富集。岩浆岩形成于大陆边缘初始裂谷的环境下,其中辉绿岩、辉长岩、玄武岩可能是Kerguelen地幔柱与岩石圈地幔相互作用的产物;英安岩的形成与硅铝质地壳的重熔有关。早白垩世岩浆岩为研究区初始矿源层的富集提供了成矿物质来源,古近纪和新近纪酸性侵入岩为研究区成矿提供了物质来源和热动力,在中基性侵入岩发育地区和酸性岩体周边构造发育区是找矿有利部位。
[Abstract]:In recent years, many scholars have paid close attention to the Cretaceous volcanic rocks in the Tethys Himalayan belt. The study area is located in the central and eastern part of the Tethys Himalayan belt. It belongs to the northern margin of Great India and is also located in the province of residual igneous rocks in Tethys. Through the study of geochemistry and geochronology of magmatic rocks, this paper analyzes its genesis and tectonic environment, which provides evidence for the Neo-Tethys Ocean expansion and the eastward extension of Tethys igneous rocks, and also points out the direction for further prospecting. The volcanic rocks in Xiawa area, Tibet are mainly composed of dolomite, trachyte and anshanian basalt. The zircon U-Pb age is 142 卤1.0 Ma.The zircon was formed in early Cretaceous. Elemental geochemistry shows that basalts are rich in Tianfeipeng mg peraluminous alkaline basalts, which are similar to OIB, and the total amount of rare earth elements 鈭，

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