泰宁地区中志留世辉绿岩脉成因及对陆内造山作用的制约  

Origin of Middle Silurian Diabase Dike in the Taining District,South China:Implications for Intracontinental Orogeny

作　　者：陈梦婷[1,2] 魏俊浩 石文杰[1,3] 李艳军 刘乃忠[4] Chen Mengting;Wei Junhao;Shi Wenjie;Li Yanjun;Liu Naizhong(Faculty of Earth Resources,China University of Geosciences,Wuhan 430074,China;Department of Earth Science,Durham University,Durham DH13LE,UK;National Demonstration Center for Experimental Mineral Exploration Education,Wuhan 430074,China;Northern Fujian Geological Team,Shaowu 354000,China)

机构地区：[1]中国地质大学资源学院,湖北武汉430074 [2]Department of Earth Science,Durham University,Durham DH13LE,UK [3]固体矿产勘查国家级实验教学示范中心,湖北武汉430074 [4]福建省闽北地质大队,福建邵武354000

出　　处：《地球科学》2020年第3期892-909,共18页Earth Science

基　　金：国家自然科学基金项目(Nos.41672083,41772071);中央高校基本科研业务费专项资金(No.CUGQYZX1708).

摘　　要：华南早古生代造山作用以武夷-云开造山带最为典型.然而,该次造山作用过程中岩石圈地幔性质及构造背景一直存在争议,还需要更多的基性岩证据.对武夷造山带中段泰宁地区何宝山辉绿岩脉开展了年代学、地球化学及Sr-Nd-Hf同位素研究.LA-ICP-MS锆石U-Pb年龄(430±3 Ma)表明辉绿岩脉形成于中志留世.岩石具有高Al2O3(15.23%~18.49%)、低Na2O(2.82%~4.21%)和K2O(1.63%~2.42%)含量特征,属亚碱性系列.稀土元素标准化图呈右倾,无明显Eu异常,显示富集大离子亲石元素(Rb、Ba、K、La、Sr)、不同程度亏损高场强元素(Ta、U、Hf、Ti).岩石具有高Nb含量(5.74×10^-6~8.45×10^-6),其(Nb/La)N和Nb/U值与富Nb岛弧玄武岩相似.全岩(87Sr/86Sr)i=0.7095~0.7109,εNd(t)=-0.8^-0.1,锆石εHf(t)=-9.2^-2.7,对应二阶段模式年龄T2DM(Hf)=1.4~1.8 Ga.地球化学、Sr-Nd及Hf同位素揭示泰宁地区基性岩浆源自富集岩石圈地幔13.3%~21.8%的熔融,但在熔融前曾受到古俯冲物质(俯冲板片熔体+5%沉积物熔体)的源区混染.武夷地区于早古生代为陆内造山环境,脉岩形成于后造山垮塌阶段,可能与冈瓦纳东缘造山作用的应力向大陆传播引起华夏地块内部俯冲有关.The Early Paleozoic orogen in South China is an intraplate orogen and represented by the Wuyi-Yunkai Orogenic Belt(WYOB).However,the nature of lithospheric mantle and tectonic setting during this orogenic process have been controversial.We present here,for the first time,geochronological,isotopic and geochemical data for the Hebaoshan diabase dike in Taining area,central WYOB.LA-ICP-MS dating on zircon of the Hebaoshan diabase dike yields an age of 430±3 Ma,suggesting the formation time of Middle Silurian.Seven samples possess high Al2O3(15.23%-18.49%)and low Na2O(2.82%-4.21%),K2O(1.63%-2.42%)contents,belonging to subalkaline rocks.The REE patterns show a negative slope due to LREE enrichment with insignificant Eu anomalies.Diabase is characterized by enrichment in Rb,Ba,K,La,Sr while depletion in Ta,U,Hf and Ti,relative to the primitive mantle.The high Nb(5.74×10^-6-8.45×10^-6)content,together with high values of(Nb/La)N and Nb/U,coincides with those of typical Nb-rich Island Arc Basalt.The Hebaoshan diabase dike,with variableεNd(t)values(-0.8--0.1),εHf(t)values(-9.2--2.7)and two-stage Hf model ages(T2DM(Hf)=1.4-1.8 Ga),was probably derived from the partial melting(13.3%~21.8%)of previously subduction-modified lithospheric mantle in the garnet-spinel olives facies and was likely formed in an intracontinental post-orogenic collapse regime related to a farfield effect from Eastern Gondwana orogeny.

关 键 词：辉绿岩脉 早古生代 陆内造山作用 武夷-云开造山带 华南 地质年代学 地球化学 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]