南秦岭土地岭早古生代粗面质火山岩成因:来自锆石U-Pb年龄、元素及Sr-Nd同位素证据  

Petrogenesis of Early Paleozoic Trachytic Volcanic Rocks in Tudiling Area,South Qinling Orogen:Evidence from Zircon U-Pb Age,Elemental and Sr-Nd Isotope Geochemistry

作　　者：周豹 王飞[2] 李一鸣 鲁显松 熊意林 魏四华 杨振[2] 刘锐[2] ZHOU Bao;WANG Fei;LI Yiming;LU Xiansong;XIONG Yilin;WEI Sihua;YANG Zhen;LIU Rui(Hubei Geological Survey,Wuhan 430034,Hubei,China;School of Earth Resources,China University of Geosciences,Wuhan 430074,Hubei,China;Hubei Geological Exploration Engineering Technology Research Center,Wuhan 430034,Hubei,China)

机构地区：[1]湖北省地质调查院,湖北武汉430034 [2]中国地质大学(武汉)资源学院,湖北武汉430074 [3]湖北省地质勘查工程技术研究中心,湖北武汉430034

出　　处：《大地构造与成矿学》2023年第3期681-694,共14页Geotectonica et Metallogenia

基　　金：湖北省地质局科技项目(KJ2020-47、KJ2020-54);国家自然科学基金项目(41002025);中央高校基本科研业务费专项资金项目(CUGL140406)联合资助。

摘　　要：南秦岭土地岭地区火山岩因富含铌钽等稀有金属元素而受到广泛关注,但目前对该类火山岩成因的研究还较为薄弱。通过对土地岭典型粗面质火山岩进行锆石U-Pb年代学、主‒微量元素及Sr-Nd同位素地球化学研究,探讨岩石成因及成岩构造背景。土地岭富铌钽火山岩主要岩石类型有霓石粗面岩、含晶屑粗面质凝灰熔岩、晶屑粗面质熔结凝灰岩、粗面质晶屑凝灰岩及沉凝灰岩。LA-ICP-MS锆石U-Pb定年表明,该火山岩成岩年龄为445±10 Ma,形成于早志留世。地球化学特征表明,火山岩样品具高硅(SiO_(2)=55.97%~66.71%)富碱(K_(2)O+Na_(2)O=8.64%~16.74%)的特征,为一套碱性火山岩;轻稀土元素显示相对富集特征((La/Yb)N=11.2~93.6)。火山岩(87Sr/^(86)Sr)i主体为0.7034~0.7057,ε_(Nd)(t)值为2.2~2.7,相应的Nd模式年龄tDM为0.77~0.89 Ga。土地岭火山岩Sr-Nd同位素组成具有洋岛玄武岩(OIB)特征,可能来自于HIMU,EMⅠ和EMⅡ的混合源区。结合其较高的Nb/U值(10.8~106.1)以及主量元素CaO、MgO、Fe_(2)O)(3)^(T)、TiO_(2)与SiO_(2)均显示负相关关系特征,土地岭赋矿火山岩应该为富集地幔来源岩浆结晶分异作用的产物,可能形成于早古生代华南板块北缘的被动大陆边缘环境。Volcanic rocks in the Tudiling area of the South Qinling orogen have attracted wide attention due to their enrichments of Nb and Ta.However,the research on the origin of these volcanic rocks is still poor.To delineate their petrogenesis and tectonic setting,zircon U-Pb geochronology,major trace elemental and Sr-Nd isotopic geochemistry of typical trachytic volcanic rocks in Tudiling were studied.The main rock types of the Tudiling Nb-Ta-rich volcanic rocks are aegirine trachyte,trachytic crystal tuffaceous lava,trachytic crystal ignimbrite,trachytic crystal tuff and tuffite.LA-ICP-MS zircon U-Pb dating yielded an age of 445±10 Ma,indicating the volcanic rock was formed in the Early Silurian.The volcanic rocks are characterized by high silica(55.97%to 66.71%)and high alkali(8.64%to 16.74%K_(2)O+Na_(2)O)contents,and belong to alkaline volcanic rocks.The light rare earth elements(LREE)are relatively enriched with(La/Yb)N ratios varying between 11.2 and 93.6.The(^(87)Sr/^(86)Sr)i andε_(Nd)(t)values of the volcanic rocks range from 0.7034 to 0.7057 and 2.2 to 2.7 respectively,with corresponding Nd model ages of 0.77 to 0.89 Ga.The Sr-Nd isotopic compositions of the Tudiling volcanic rocks are similar to that of oceanic island basalt(OIB),indicating that the source region may be dominated by the mantle component of HIMU,mixed with EMI and EMⅡcomponents.Combined with the high Nb/U ratio(10.8 to 106.1)and the negative correlation between CaO,MgO,Fe_(2)O)(3)^(T),TiO_(2)and SiO_(2),the Tudiling ore-bearing volcanic rocks should be the products of crystallization and differentiation of enriched mantle derived magma.The Tudiling Nb-Ta-rich volcanic rocks may have formed in a passive continental margin environment of the northern margin of the South China Block in the Early Paleozoic.

关 键 词：锆石U-PB年龄 元素地球化学 SR-ND同位素 富铌钽火山岩 土地岭 南秦岭 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]