摘要
本研究聚焦于喜马拉雅造山带亚东地区首次发现的锂辉石伟晶岩原位露头,通过详细的野外考察、室内岩相学观察、全岩主微量分析以及同位素定年等方法,对该伟晶岩进行了系统研究。锂辉石伟晶岩脉近水平产出于告乌岩体北部的曲清塘附近,海拔在3650~3931m之间,出露宽度不等,大多锂辉石颜色以无色透明、灰白色为主,具有较好的柱状晶型,粒度整体变化较大,且未出现明显内部分带结构;矿物组成包括钠长石、正长石、石英、白云母以及锂辉石、透锂长石、绿柱石、锡石、铌钽铁矿等锂-铍-铌-钽-锡稀有金属矿物,其中锂辉石分布较不均匀,含量在2%~25%之间。岩石地球化学特征显示,锂辉石伟晶岩具有高硅强过铝富碱、贫钙铁镁磷的特点,并表现出富集Rb、Cs、Ta、Hf,亏损Sr、Th、Eu、Ti等元素的特征,其中稀有金属元素Li、Rb、Cs含量最高分别达到16017×10^(-6)、2517×10^(-6)和819×10^(-6);稀土元素呈轻稀土富集、轻重稀土分馏明显,具明显负Eu异常的四分组效应,均表明亚东地区岩浆分异演化程度高。同位素定年结果显示,亚东锂辉石伟晶岩独居石^(208)Pb/^(232)Th年龄可分为21Ma和18~17Ma两个阶段,在^(207)Pb/^(206)Pb-238 U/^(206)Pb的Tera-Wasserburg谐和图中获得锡石的下交点年龄为18~16Ma;不含锂辉石伟晶岩样品获得的独居石^(208)Pb/^(232)Th年龄均在22~21Ma之间。亚东地区锂辉石产状多样,存在粗大长柱状锂辉石与针状锂辉石。成矿伟晶岩的产出明显受藏南拆离系的控制,呈NW-SE向展布,与亚东剪切带延伸方向一致,沿亚东剪切带间断式出露,其形成过程与藏南拆离系的活动周期相一致,产出特征与琼嘉岗(普士拉)锂辉石伟晶岩和嘎波锂辉石伟晶岩等具有相似性,进一步反映了喜马拉雅带的锂成矿作用具有较好的空间一致性。亚东锂辉石伟晶岩的发现为喜马拉雅稀有金属成矿研究与锂资源勘查提供了基础地质资料,有助于理解构造-岩浆活动与稀有金属成矿的耦合关系,同时为今后在喜马拉雅带内寻找相关稀有金属矿床提供了重要参考。
This study focuses on the firstly discovered spodumene pegmatites in the Yadong area of the Himalayan orogen.Through detailed field investigations,petrographic observations,whole-rock major and trace element analyses,and U-Pb isotope dating,the pegmatites have been systematically studied.The spodumene pegmatite veins are nearly horizontally distributed near Quqingtang in the northern part of the Gaowu pluton,at elevations ranging from 3650m to 3931m.The outcrop widths vary,with most spodumene crystals being colorless,transparent,or grayish-white,exhibiting well-formed columnar shapes.The grain size varies significantly,and no obvious internal zoning structure is observed.The mineral assemblage includes albite,orthoclase,quartz,muscovite,as well as spodumene,petalite,beryl,cassiterite,columbite,which are rare metal minerals containing lithium,beryllium,niobium,tantalum,and tin.Spodumene is unevenly distributed,with contents ranging from 2%to 25%.Geochemical characteristics reveal that the spodumene pegmatites are characterized by high silica,strong peraluminous,alkali enrichment,and depletion in calcium,iron,magnesium,and phosphorus.It also shows the enrichment of Rb,Cs,Ta,and Hf,and depletion in Sr,Th,Eu,and Ti.Notably,the rare metal elements Li,Rb,and Cs reach high concentrations,with maximum values of 16017×10^(-6),2517×10^(-6),and 819×10^(-6),respectively.The rare earth elements exhibit light rare earth elements enrichment,significant fractionation between light and heavy rare earth elements,and a pronounced negative Eu anomaly with a tetrad effect,all indicating a high degree of magmatic differentiation and evolution in the Yadong region.Isotopic dating results show that the monazite^(208)Pb/^(232)Th ages of the Yadong spodumene pegmatites can be divided into two stages:21Ma and 18~17Ma.The lower intercept ages of cassiterite in the^(207)Pb/^(206)Pb-238 U/^(206)Pb Tera-Wasserburg concordia diagram range between 18Ma and 16Ma.The monazite^(208)Pb/^(232)Th ages of spodumene-free pegmatite samples range between 22Ma and 21Ma.In the Yadong region,spodumene exhibits diverse occurrences,including large prismatic crystals and acicular spodumene.The occurrence of mineralized pegmatites in the Yadong region is clearly controlled by the South Tibetan Detachment System(STDS),trending NW-SE,consistent with the strike of the Yadong Cross Structure(YCS),and they are discontinuously exposed along the YCS,and their formation process is consistent with the activity period of the STDS.The characteristics of these pegmatites are similar to those of the Qunggya Kang(Pusi La)and Gabo spodumene pegmatites,further reflecting the spatial consistency of lithium mineralization in the Himalayan orogen.The discovery of spodumene pegmatites in Yadong provides fundamental geological data for the study of rare metal mineralization and lithium resource exploration in the Himalayas,contributing to the understanding of the coupling relationship between tectonic-magmatic activities and rare metal mineralization.It also offers important references for future exploration of related rare metal deposits in the Himalayan orogen.
作者
赵向英
刘小驰
邢璐遥
李雪震
赵俊兴
胡方泱
吴福元
ZHAO XiangYing;LIU XiaoChi;XING LuYao;LI XueZhen;ZHAO JunXing;HU FangYang;WU FuYuan(State Key Laboratory of Lithospheric and Environmental Coevolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《岩石学报》
北大核心
2025年第9期3000-3018,共19页
Acta Petrologica Sinica
基金
中国科学院战略性先导科技专项(XDA0430101)
第二次青藏高原综合科学考察研究(2019QZKK0802、2022QZKK0203)联合资助。
作者简介
第一作者:赵向英,女,2001年生,硕士生,矿物学、岩石学、矿床学专业,E-mail:zhaoxiangying24@mails.ucas.ac.cn;通讯作者:刘小驰,男,1985年生,副研究员,从事花岗岩成因与造山带演化研究,E-mail:liuxiaochi@mail.iggcas.ac.cn。
