滇西雪龙山杂岩新生代高钾花岗质岩脉锆石U-Pb年代学、Hf同位素组成与区域构造意义  

ZIRCON U-Pb GEOCHRONOLOGY,Hf ISOTOPIC COMPOSITION AND REGIONAL TECTONIC IMPLICATION OF CENOZOIC HIGH POTASSIC GRANITIC INTRUSIONS IN THE XUELONGSHAN MASSIF,WESTERN YUNNAN

作　　者：陈玮 熊富浩[1] 赵涵[1] 蒋文忠 CHEN Wei;XIONG Fuhao;ZHAO Han;JIANG Wenzhong(Chengdu University of Technology,Chengdu 610059,Sichuan,China;SinoProbe Laboratory of Chinese Academy of Geological Sciences,Beijing 100029,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]自然资源部深地科学与探测技术实验室,北京100029

出　　处：《矿物岩石》2024年第2期12-29,共18页Mineralogy and Petrology

基　　金：自然资源部深地科学与探测技术实验室开放基金(项目编号:SinoProbe Lab202226)。

摘　　要：新生代印度-欧亚板块碰撞后,增厚的羌塘-三江特提斯区域地壳因造山后伸展作用形成一系列高钾岩浆。本次研究以雪龙山杂岩中的糜棱岩化高钾花岗质岩脉为研究对象,通过构造变形解析、锆石U-Pb与Hf同位素研究、岩石地球化学与岩石成因分析,以期对哀牢山-红河剪切带北段新生代构造演化进行限定。结果表明,3个花岗质岩脉锆石新生代U-Pb年龄分别为34.8±0.4Ma,35.4±0.3Ma和32.6±0.2Ma,反映了岩浆就位时间;锆石εHf(t)值分别为+7.8~+8.6,+3.7~+7.0和+6.3~+9.2,二阶段模式年龄分别为563~658Ma,664~876Ma和524~706Ma,表明其源区为新生镁铁质下地壳。3个花岗质岩脉岩石地球化学特征相似,ω(SiO_(2))(70.14%~73.74%)较高ω(MgO)(0.07%~0.84%)、ω(Y)(3.92×10^(-6)~8.66×10^(-6))、ω(Yb)(0.27×10^(-6)~0.77×10^(-6))含量较低,具有高Sr/Y比值(42.54~129.18),低Na_(2)O/K_(2)O比值(0.82~1.66)特征,呈现出(类)埃达克质岩浆属性。综合分析表明,在始新世-渐新世,三江地区增厚的下地壳在后续重力失稳作用下发生碰撞后板片断离,诱发深部地幔物质上涌和底侵加厚地壳,进而促使加厚地壳熔融,形成(类)埃达克质高钾岩浆。在岩浆上涌过程中,捕获或继承了古特提斯洋演化不同阶段的锆石。结合岩石变形分析,哀牢山-红河剪切带新生代左行走滑剪切应在32.6Ma之后。This paper presents a study of structural deformation,zircon U-Pb and Hf isotopes,rock geo-chemistry,and petrogenesis analysis to understand the mylonitic high-potassium granitic dykes in the Xue-longshan complex,aiming to constrain the Cenozoic tectonic evolution of the northern section of the Ailaoshan-Honghe Shear Zone.The zircon U-Pb dating of three granitic dyke samples reveals Cenozoic a-ges of 34.8±0.4 Ma,35.4±0.3 Ma,and 32.6±0.2 Ma.The EHr(t)values of the zircons range from+7.8 to+8.6,+3.7 to+7.0,and+6.3 to+9.2,respectively,with second-stage model ages between 563-658 Ma,664-876 Ma,and 524-706 Ma,suggesting that the magma source is juvenile mafic lower crust.Geochemical analysis shows that the three granitic dykes have similar characteristics,with high ω(SiO_(2))content(70.14%-73.74%)and low ω(MgO)content(0.07%-0.84%),ω(Y)(3.92×10^(-6)8.66×10^(-6))and(Yb)(0.27 ×10^(-6)-0.77 ×10^(-6)).They also exhibit high Sr/Y ratios(42.54-129.18)and low Na_(2)O/K_(2)O ratios(0.82-1.66),indicative of adakitic or adakitic-like magmatic proper-ties.Comprehensive analysis indicates that during the Eocene-Oligocene,the thickened lower crust in the Sanjiang area experienced gravitational instability.The subsequent collision-induced separation of plate fragments triggered the upwelling of deep mantle material,leading to the thickening and melting of the crust.This process generated adakitic or adakitic-like high-potassium magma.Zircons from different sta-ges of the ancient Tethys Ocean's evolution were captured or inherited during magmatic emplacement.Combining this with rock deformation analysis,it is proposed that the Cenozoic left-lateral strike-slip shear of the Ailaoshan-Honghe Shear Zone occurred after 32.6 Ma.

关 键 词：雪龙山杂岩 锆石U-Pb与Hf同位素分析 岩石地球化学 高钾花岗岩脉 哀牢山-红河剪切带 

分 类 号：P579[天文地球—矿物学]