| 西藏拉萨地块东部尼木—加查地区林子宗群火山岩年代学、地球化学特征及其构造意义 |
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| 引用本文： | 韦天伟,杨锋,康志强,韦乃韶,刘迪,曹延,李岱鲜,陈欢,陈林华.西藏拉萨地块东部尼木—加查地区林子宗群火山岩年代学、地球化学特征及其构造意义[J].现代地质,2019,33(4):715-726. |
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| 作者姓名： | 韦天伟 杨锋 康志强 韦乃韶 刘迪 曹延 李岱鲜 陈欢 陈林华 |
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| 作者单位： | 1.桂林理工大学 地球科学学院,广西有色金属隐伏矿床勘查及材料开发协同创新中心,广西 桂林 5410042.重庆市地质矿产勘查开发局107地质队,重庆 401120 |
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| 基金项目： | 国家重点研发计划项目(2016YFC0600407);国家自然科学基金项目(41863005);国家自然科学基金项目(41463001);广西自然科学基金项目(2016GXNSFAA380012) |
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| 摘 要： | 拉萨地块广泛分布中—新生代岩浆活动,研究其对于认识新特提斯洋的演化和理解整个青藏高原的形成过程有着重要意义。对拉萨地块东部尼木—加查地区比马组火山岩进行了年代学与元素地球化学研究,结果显示该比马组火山岩LA-ICP-MS锆石U-Pb年龄为55.2~57.6 Ma,明显晚于已发表的比马组火山岩年龄177~195 Ma,而与林子宗群火山岩年龄(30.4~70.0 Ma)相符。因此,该地区原来认为的比马组火山岩可能需要重新厘定为林子宗群年波组火山岩。研究区火山岩主体为玄武岩、玄武安山岩、安山岩和英安岩,属中、高钾钙碱性系列。地球化学特征显示火山岩整体上富集大离子亲石元素Rb、Th、U等,Nb、Ta、Zr、Ti等高场强元素则表现明显的负异常,具有典型的岛弧火山岩特征。稀土元素配分模式主要表现为轻稀土元素右倾型,Eu表现出无异常到中等的负异常。此外,研究区年波组火山岩年龄晚于拉萨地块中西部年波组形成时代,结合前人的研究成果,可能指示印度与亚洲大陆的碰撞具有西早东晚的特点。
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| 关 键 词： | LA-ICP-MS锆石 U-Pb定年 地球化学 年波组 林子宗群 拉萨地块 |
| 收稿时间： | 2018-05-29 |
| 修稿时间： | 2019-02-02 |
Geochronology,Geochemistry and Tectonic Significance of Linzizong Group Volcanic Rocks in the Nimu-Jiacha Area,Eastern Lhasa Block,Tibet,China |
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| WEI Tianwei,YANG Feng,KANG Zhiqiang,WEI Naishao,LIU Di,CAO Yan,LI Daixian,CHEN Huan,CHEN Linhua.Geochronology,Geochemistry and Tectonic Significance of Linzizong Group Volcanic Rocks in the Nimu-Jiacha Area,Eastern Lhasa Block,Tibet,China[J].Geoscience——Journal of Graduate School,China University of Geosciences,2019,33(4):715-726. |
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| Authors: | WEI Tianwei YANG Feng KANG Zhiqiang WEI Naishao LIU Di CAO Yan LI Daixian CHEN Huan CHEN Linhua |
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| Institution: | 1. School of Earth Science, Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi, Guilin University of Technology, Guilin, Guangxi 541004, China2. 107 Geological Team, Chongqing Bureau of Geology Mineral Resources Exploration and Development, Chongqing 401120, China |
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| Abstract: | Lhasa block is featured by extensive Mesozoic-Cenozoic magmatism, which is important for understanding the Neo-Tethyan evolution and the tectonic history of the Tibetan plateau. In this paper, LA-ICP-MS zircon U-Pb dating and whole-rock geochemical analyses of the Bima Formation volcanic rocks in the Nimu-Jiacha area (eastern Lhasa block) were carried out. Zircon U-Pb ages of the Bima Formation volcanic rock are about 55.2-57.6 Ma, which are significantly younger than the published Pima volcanic rock age of 177-195 Ma, and are coeval with the Linzizong Group volcanic rocks (30.4-70.0 Ma). Accordingly, the Bima Formation that was originally thought to be in the area should be redefined as Nianbo Formation of the Linzizong Group. The main volcanic rocks in the study area are basalt, basaltic andesite, andesite and dacite, belonging to the middle-to high-K calc-alkaline series. The volcanic rocks are enriched in LILEs (e.g., Rb, Th, U) and show clear negative anomalies of HFSEs (e.g., Nb, Ta, Zr, Ti), with typical island arc geochemical affinities. The REE patterns reveal LREE enrichments, and no or moderately-negative Eu anomaly. In addition, the Nianbo Formation volcanic rocks in the study area are younger than the Nianbo Formation in the middle-western Lhasa block. Combined with published information, it is indicated that the India-Asia collision progressed from west to east. |
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| Keywords: | zircon LA-ICP-MS U-Pb dating geochemistry Nianbo Formation Linzizong Group Lhasa block |
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