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现代地质 ›› 2021, Vol. 35 ›› Issue (05): 1194-1205.DOI: 10.19657/j.geoscience.1000-8527.2021.065

• 岩石学 • 上一篇    下一篇

新特提斯洋晚白垩世演化特点:来自泽当共国日二长花岗岩年代学、地球化学及Sr-Nd同位素证据

张志平1,2(), 钟康惠1, 单树成1, 郑鑫1,3, 黄浩震1, 严钊1   

  1. 1.成都理工大学 地球科学学院,四川 成都 610059
    2.甘肃省地质矿产勘查开发局第三地质矿产勘查院,甘肃 兰州 730050
    3.重庆市地质矿产勘查开发局川东南地质大队,重庆 400038
  • 收稿日期:2020-02-24 修回日期:2021-02-15 出版日期:2021-10-10 发布日期:2021-11-04
  • 作者简介:张志平,男,高级工程师,硕士研究生,1985年出生,矿物学、岩石学、矿床学专业,主要从事区域地质矿产调查工作。Email: zhangzhiping@stu.cdut.edu.cn
  • 基金资助:
    中国地质调查局项目“冈底斯-喜马拉雅铜矿资源基地项目”(121201010000150014-46);中国地质调查局项目“冈底斯-喜马拉雅铜矿资源基地项目”(DD20160015-08)

Late Cretaceous Evolution of the Neo-Tethys:Evidence from Geochronology, Geochemistry, and Sr-Nd Isotopes of Gongguori Monzogranite in Zedang

ZHANG Zhiping1,2(), ZHONG Kanghui1, SHAN Shucheng1, ZHENG Xin1,3, HUANG Haozhen1, YAN Zhao1   

  1. 1. College of Earth Science, Chengdu University of Technology, Chengdu, Sichuan 610059, China
    2. The Third Institute of Geology and Minerals Exploration, Gansu Provincial Bureau of Geology and Minerals Exploration and Development, Lanzhou, Gansu 730050, China
    3. Southeast Sichuan Geological Team of Chongqing Bureau of Geological and Mineral Exploration and Development, Chongqing 400038, China
  • Received:2020-02-24 Revised:2021-02-15 Online:2021-10-10 Published:2021-11-04

摘要:

为加深对西藏泽当地区新特提斯洋演化的认识,对西藏泽当蛇绿混杂岩带内的共国日二长花岗岩进行了岩石学、岩石地球化学、同位素及年代学等研究,研究显示:共国日二长花岗岩岩体规模小、岩性稳定,LA-ICP-MS锆石U-Pb年龄为(90.40±0.68)Ma,属晚白垩世;岩石地球化学具高硅、富铝、富钾、低钛和准铝质钙碱性花岗岩特征;轻稀土富集、重稀土亏损,具明显的负Eu异常,微量元素表现为相对富集Rb、K、Ba、Th、U等大离子亲石元素,显著亏损Nb、P、Ti等高场强元素;(87Sr/86Sr)i=0.705 708~0.706 284,(143Nd/144Nd)i=0.512 689~0.512 716,εNd(t)=2.00~2.51。以上特征表明,位于泽当蛇绿混杂岩带内的共国日二长花岗岩属于I型花岗岩,由正常岛弧岩浆形成,应为晚白垩世新特提斯洋向北俯冲形成的岛弧环境下俯冲带上部地壳部分熔融的产物,其不属于泽当蛇绿岩的组成部分,表明在90 Ma前泽当洋内弧已经消失。

关键词: 西藏泽当, 蛇绿岩, 二长花岗岩, 岩石地球化学, 锆石U-Pb, 岩石成因

Abstract:

To deepen our understanding on the evolution of the Neo-Tethys ocean in Zedang area, Tibet, a study of the petrology, petrochemistry, isotope and geochronology of the Gongguori monzogranite in the Zedang ophiolitic mélange belt is carried out. The result shows that it is small and has similar lithology. LA-ICP-MS zircon U-Pb dating on the pluton yielded Late Cretaceous crystallization age of (90.40±0.68) Ma. The Gongguori monzogranite is rich in Si, Al, and K and Ti-poor, and is metaluminous, calc-alkaline to alkaline. The rocks show LREE enrichments, HREE depletions, and negative Eu anomaly. The monzogranite is also enriched in LILEs (e.g.,Rb, K, Ba, Th, U) and depleted in HSFEs (e.g., Nb, P, Ti). The rocks have (87Sr/86Sr)i=0.705,708 to 0.706,284, (143Nd/144Nd)i=0.512,689 to 0.512,716, and positive εNd(t)=2.00 to 2.51. Based on the geochronological and geochemical characteristics of the Gongguori pluton, this study demonstrates that the Gongguori monzogranite was formed by normal island arc I-type granitic magmatism. The Gongguori monzogranite may have been a partial melting product of the upper crust, which was formed by the Late Cretaceous north-dipping subduction of the Neo-Tethys. The Gongguori monzogranite is unlikely part of the Zedang ophiolite, and the Zedang intra-oceanic arc may have disappeared before 90 Ma.

Key words: Zedang, Tibet, ophiolite, monzogranite, geochemistry, zircon U-Pb dating, petrogenesis

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