冈底斯弧西部林子宗群年波组火山岩锆石U-Pb年代学、岩石成因及其指示  

Zircon U-Pb geochronology, genesis for Nianbo Formation volcanic rocks of Linzizong Group in the western part of Gangdese arc and its implication

作　　者：呼建雄 陈建林[3,4] 姚胜 曾云川 雷鸣[3] 熊秋伟 刘希军 HU Jian-xiong;CHEN Jian-lin;YAO Sheng;ZENG Yun-chuan;LEI Ming;XIONG Qiu-wei;Liu Xi-jun(Academy of Regional Geological Survey and Mineral Resources Exploration of Shaanxi Co. Ltd., Xianyang 712000, China;China University of Geosciences, Beijing 100083, China;State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou510640, China;CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin 541004, China)

机构地区：[1]陕西地矿区研院有限公司,陕西咸阳712000 [2]中国地质大学(北京),北京100083 [3]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640 [4]中国科学院青藏高原地球科学卓越创新中心,北京100101 [5]桂林理工大学地球科学学院广西隐伏金属矿产勘查重点实验室,广西桂林541004

出　　处：《地球化学》2018年第6期699-711,共13页Geochimica

基　　金：国家重点研发计划国家深部专项专题(2016YFC0600305);中国地质大调查冈底斯西北缘晚白垩世斑岩铜矿带综合调查(DD20160024-06);国家自然科学基金(41573024;41873037);广西隐伏金属矿产勘查重点实验室开放基金(17-140-27-K01)

摘　　要：冈底斯弧广泛发育的林子宗群火山岩被认为是新特提斯洋北向俯冲及随后印度与欧亚大陆相互碰撞作用过程的响应,对探讨从大洋俯冲到大陆碰撞的转换有一定的指示意义。本研究通过冈底斯弧西部措勤地区杰萨错林子宗群年波组一段火山岩地球化学和锆石U-Pb年代学研究结果显示,研究区形成于(59.24±0.70)Ma的流纹岩在稀土元素中具有明显Eu负异常,在原始地幔标准化蛛网图中显示Nb、Ta、Ti等元素的亏损,以及高的Y含量和低的La/Yb比值。上述杰萨错年波组火山岩地球化学特征指示其形成于陆缘弧环境,很可能为岛弧岩浆在上升过程中经历斜长石和钾长石等矿物分异的产物。同时,研究区年波组酸性火山岩具有与冈底斯弧中西部年波组火山岩相类似的主元素、微量元素含量及其分布范围(如K_2O、Th等的含量),暗示它们有着相似的物质源区。结合前人的研究内容,初步认为冈底斯弧东西向广泛发育的林子宗群年波组火山岩几乎同期形成于陆缘弧环境中,为北向俯冲的新特提斯大洋板片回转的产物。The volcanic successions of the Linzizong Group are widely distributed along the Gangdese Arc,which has been related to the northward subduction of the Neotethyan oceanic slab and subsequent collision between the Indian and Eurasian continents.It is important to understand the change from subduction of oceanic slab to continental collision.In this paper,new geochronology and geochemical data have been presented for the rhyolite of the Nianbo Formation,which cropped from Jiesacuo of the Cuoqin region,western Gangdese Arc.Zircon U-Pb dating suggests that they were generated at(59.2±0.7)Ma.The studied samples show high Y contents and low La/Yb ratios,a remarkable Eu anomaly,and depletion in high field strength elements(HFSEs:e.g.Nb,Ta,Zr,Hf,and Ti),indicating that the rhyolite is a result of fractional crystallization of plagioclase and potash feldspar of the primitive magma generated in a continental marginal arc.Additionally,the similarly variable concentration range of K2O,Th,and other elements of the volcanics of the Nianbo Formation in western,middle,and eastern Gangdese arc indicates that they originated from the same source.Considering previous studies,it is suggested that the volcanic rocks of the Nianbo Formation of the Linzizong Group developed at the same period,triggered by a rollback of the north-dip Neotethyan oceanic slab.

关 键 词：冈底斯弧 林子宗群 年波组 锆石U-PB 流纹岩 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]