南秦岭唐家沟英云闪长岩年代学及岩石地球化学特征  

GEOCHEMICAL AND GEOCHRONOLOGICAL CHARACTERISTICS OF TANGJIAGOU TONALITES IN THE SOUTH QINLING

作　　者：王东升[1] 王宗起[1] 王涛[2] 张英利[1] 陈雷[1] 武昱东[1] 张玉涛[1] 

机构地区：[1]中国地质科学院矿产资源研究所,国土资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质科学院地质研究所,北京100037

出　　处：《矿物岩石》2016年第2期71-81,共11页Mineralogy and Petrology

基　　金：自然科学基金(41402180);国土资源部中国地质调查局项目(12120113069000)

摘　　要：南秦岭马道地区唐家沟英云闪长岩主要由石英、斜长石、钾长石、黑云母及少量角闪石等组成。地球化学特征表明,岩体w(SiO_2)介于59.23%~65.74%,w(K_2O)=1.53%~6.57%,w(Na_2O)=3.69%~5.81%,里特曼指数σ除一个样品外均小于4,属钙碱性花岗岩系列。w(Al_2O_3)=15.37%~18.37%,A/CNK介于0.90~1.02,A/NK介于1.39~1.70,属准铝-过铝质花岗岩。w(FeO)=1.58%~3.97%,w(Fe_2O_3)=1.35%~2.42%,w(MgO)=1.08%~3.11%,w(TiO_2)=0.50%~0.84%,w(P_2O_5)=0.14%~0.30%。稀土元素含量为128.11×10^(-6)~152.39×10^(-6),相对富集轻稀土(LREE=112.24×10^(-6)~145.15×10^(-6)),亏损重稀土(HREE=7.08×10^(-6)~15.87×10^(-6))。LREE/HREE为7.07~20.50,(La/Yb)_N值为6.88~44.26,样品不具有明显的Eu异常(δEu=0.68~0.96)和Ce异常(δCe=0.83~0.93)。样品富集大离子亲石元素(Rb,Th,U等)、强烈亏损高场强元素(Nb,Ta,Ti),类似于钙碱性火山弧花岗岩的地球化学特征。阴极发光CL图像显示岩体锆石具有核-边结构,结合锆石原位微量元素研究认为,核部锆石为继承下来的原岩锆石,时代为(810 Ma±4.8 Ma),而边部锆石为深熔锆石,年龄为(205 Ma±2.6 Ma)。结合前人资料,认为唐家沟英云闪长岩形成于新元古代秦岭洋俯冲阶段,在晚三叠世秦岭洋闭合期间该岩体受到再次改造。The Tangjiagou tonalities mainly consist of quartz,plagioclase,K-plagioclase and biotite with minor amphiboles.Geochemical analysis shows that the tonalities displays w（SiO2）content between 59.23% and 65.74%,w（K2O）content between 1.53% and 6.57%,w（Na2O）content of 3.69%-5.81%,σindex of 1.64 to 3.63 except for one sample,indicating that it belongs to calc-alkaline series.It also reveals that the Tangjiagou tonalities have w（Al2O3）content between 15.37% and 18.37%,A/CNK ratio of 0.90 to 1.02,A/NK ratio of 1.39 to 1.70,suggesting the metaluminous-peraluminous feature.The rocks show w（FeO）content between 1.58%and 3.97%,w（Fe2O3）content between 1.35% and 2.42%,w（MgO）content of 1.08% -3.11%,w（TiO2）content of 0.50% -0.84%,w（P2O5）content of 0.14% -0.30%.The total REE values of the tonalities vary in the range of 128.11×10^-6 to 152.39×10^-6 and the chondritenormalized REE patterns are characterized by LREE enrichment（LREE=112.24×10^-6^-145.15×10^-6）and depletion in HREE（HREE=7.08×10^-6-15.87×10^-6）without insignificant Eu anomalies（δEu=0.68-0.96）and Ce anomalies（δCe=0.83-0.93）.The values of LREE/HREE and（La/Yb）Nis 7.07-20.50 and 6.88-44.26,respectively.Trace elements spider diagram shows that tonalities are enriched in large ion lithophile elements（LILE,Rb,Th,U）and intensively depleted in high field strength elements（HSFE,Nb,Ta,Ti）,similar to the geochemical characteristics of calc-alkline magmatites in volcanic arc setting.CL images of zircons show a distinct core-edge structure which most zircons have obvious oscillatory zoning developed within core and weak grayish zoning edge,suggesting that cores of zircons are magmatic in origin and the edges of zircons may result from anatectic event.LA-ICP MS dating yields 810Ma±4.8Ma age for the protoith of tonalities and anatectic event records of 205Ma±2.6Ma.On the basis of previous studies and regional tectonic setting,it is proposed that the Tangjiagou tonalites formed during southward subduction of Qin

关 键 词：南秦岭增生杂岩带 唐家沟英云闪长岩 地球化学 LA-ICP-MS锆石定年 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]