北喜马拉雅带早侏罗世OIB型玄武岩发现:锆石U-Pb年龄、地球化学及岩石成因  

Discovery of Early Jurassic OIB-type basalts in the northern Himalayas:Zircon U-Pb age, geochemistry and petrogenesis

作　　者：魏永峰 肖倩茹[1] 吴建鑫[1] 肖渊甫 杨剑红[2] 林美英 WEI Yongfeng;XIAO Qianru;WU Jianxin;XIAO Yuanfu;YANG Jianhong;LIN Meiying(College of Earth Sciences,Chengdu University of Technology,Chengdu,610059;Regional Geological Surveying Party,Sichuan Bureau of Geology and Mineral Resources Development,Chengdu,610213;Observation and Research Station of Refractory Gold Ores in Muli,Sichuan,MNR,Muli,Sichuan,615800)

机构地区：[1]成都理工大学地球科学学院,成都610059 [2]四川省地质矿产勘查开发局区域地质调查队,成都610213 [3]自然资源部四川木里难选冶金矿野外科学观测研究站,四川木里615800

出　　处：《地质论评》2022年第2期452-468,共17页Geological Review

基　　金：中国地质调查局冈底斯—喜马拉雅铜矿资源基地调查项目(编号:12120115022901、121201010000150014-21、DD20160015-01)的成果。

摘　　要：早侏罗世库局OIB型玄武岩分布于北喜马拉雅带东端,其作为夹层产出于早侏罗统普普嘎组下部层位,围岩为粉砂质板岩、泥岩。代表性样品玄武岩的LA-ICP-MS锆石U-Pb定年显示,锆石24个分析点的n(^(206)Pb)/n(^(238)U)年龄为115.2~240.9 Ma,n(^(206)Pb)/n(^(238)U)加权平均年龄为190.8±1.2 Ma(n=16,MSWD=3.6),为早侏罗世早期,代表了岩浆的结晶时代。地球化学特征表明,岩石具有低K_(2)O、中MgO及高TiO_(2)、P_(2)O_(5)、TFeO特征,(La/Yb)_(N)为4.4~10.3,δEu=0.89~1.07,富集Rb、Ba、Th等大离子亲石元素及Nb、Ta、Zr、Hf、Ti等高场强元素,为大陆边缘裂谷背景的具有OIB型地球化学特征的拉斑玄武岩。库局OIB型玄武岩与含石榴子石、尖晶石二辉橄榄岩部分熔融(Gt>Sp)有关,显示出岩石圈地幔物质的印记。岩石成因模式可以解释为正在孕育的地幔柱诱导的上涌软流圈物质与岩石圈地幔物质混合后在拉张背景下发生减压熔融的产物,这种地幔热柱或热点可能与Kerguelen热点的早期活动有联系,岩浆演化过程中发生了橄榄石和单斜辉石的分离结晶作用,在侵位过程中遭受了一定程度下地壳混染。早侏罗世库局OIB型玄武岩的发现填补了北喜马拉雅带东端早侏罗世岩浆活动记录,为认识特提斯喜马拉雅带中段早侏罗世构造演化提供基础资料。Objectives:The Early Jurassic OIB-type basalts reported in this article are discovered in the Northern Himalayas belt,where there have been few reports of Early Jurassic volcanic magmatism so far.At the same time,due to the lack of systematic petrological,geochemical and chronological studies,the understanding of its nature is relatively vague,resulting in a large difference in the age of the(volcanic rock)strata,resulting in stratigraphic division,the eastern extension of the northern Himalayan stratigraphic division has been unresolved.And become the focus of long-term controversy.This article attempts to explore the genesis and tectonic background of OIB-type basalts in the Early Jurassic,and to provide basic data for understanding the Early Jurassic tectonic evolution in the middle section of the Tethys Himalayas.Methods:On the basis of field investigation,according to the zircon U-Pb age,combined with geochemical characteristics.Results:The Early Jurassic OIB-type basalts in Kuju are distributed at the eastern end of the Northern Himalayas.They are produced as interlayers in the lower layer of the Early Jurassic Pupuga Formation.The surrounding rocks are silty slate and mudstone.The LA-ICP-MS zircon U-Pb dating of a representative sample of basalt shows that the n(^(206)Pb)/n(^(238)U)age of the 24 analysis points of zircon is 115.2~240.9 Ma,and the weighted average age of n(^(206)Pb)/n(^(238)U)is 190.8±1.2 Ma(n=16,MSWD=3.6),is the early Early Cretaceous,representing the crystallization age of magma.The geochemical characteristics show that the rock has the characteristics of low K_(2)O,medium MgO and high TiO_(2),P_(2)O_(5),TFeO,(La/Yb)_(N) is 4.4~10.3,δEu=0.89~1.07,and it is rich in Rb,Ba,Th and other large ion philanthropists Elements and high-field-strength elements such as Nb,Ta,Zr,Hf,Ti,etc.,are basalts with OIB-type geochemical characteristics in the background of continental margin rifts.OIB-type basalt in Kuju is related to the partial melting of garnet and spinel-bearing peridotite(Gt>Sp),showing

关 键 词：OIB型玄武岩 锆石U-PB年龄 地球化学 早侏罗世 北喜马拉雅带 西藏库局 

分 类 号：P534.52[天文地球—古生物学与地层学] P588.145[天文地球—地质学] P597.3