大兴安岭中段晚三叠世安第斯型安山岩:蒙古-鄂霍茨克大洋板片南向俯冲作用的产物  

The Late Triassic Andean-type andesite from the central Great Xing'an Range: Products of the southward subduction of the Mongol-Okhotsk oceanic plate

作　　者：纪政[1] 葛文春[1] 杨浩[1] 毕君辉[1] 于倩[1] 董玉[1] JI Zheng;GE WenChun;YANG Hao;BI JunHui;YU Qian;DONG Yu(College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2018年第10期2917-2930,共14页Acta Petrologica Sinica

基　　金：国家重点研发计划"深地资源勘查开采"重点专项(2016YFC0600403)资助

摘　　要：本文报道了大兴安岭中段火龙沟地区晚三叠世安山岩的锆石U-Pb年龄、Lu-Hf同位素组成以及全岩地球化学数据,以揭示蒙古-鄂霍茨克大洋板片早中生代期间南向俯冲作用的过程。火龙沟地区安山岩的锆石均呈自形-半自形,具有典型的振荡生长环带和高Th/U(0.48~1.47)比值的特征,暗示其为岩浆成因锆石。锆石LA-ICP-MS U-Pb同位素定年结果显示,火龙沟地区安山岩形成于236±1Ma的晚三叠世。这些晚三叠世安山岩的Si O_2含量为51.44%~66.67%,全碱(Na_2O+K_2O)含量为5.01%~6.88%,Al_2O_3含量为13.14%~19.20%,Fe_2O_3~T含量为5.11%~9.55%,Ti O_2含量为0.65%~1.66%,具有较高的MgO(2.15%~4.64%)、Cr(43.7×10^(-6)~212.0×10^(-6))和Ni(20.2×10^(-6)~100.0×10^(-6))含量以及Mg~#值(45~55),为钙碱性系列岩石。安山岩样品富集大离子亲石元素(Rb、K、Sr等)和轻稀土元素,亏损高场强元素(Nb、Ta、Ti等)和重稀土元素,且具有微弱的Eu异常(δEu=0.84~1.13),与俯冲带岩浆岩地球化学特征相似。安山岩中的锆石ε_(Hf)(t)值为+8.9^+11.6,相应的Hf同位素一阶段模式年龄(t_(DM1))为525~414Ma。上述特征表明火龙沟地区晚三叠世安山岩岩浆可能起源于俯冲流体交代的亏损地幔楔,源区可能还存在少量俯冲沉积物的贡献,并在岩浆演化的过程中经历了角闪石、斜长石和磷灰石等矿物的分离结晶作用。结合区域地质资料,认为研究区晚三叠世安山岩形成于蒙古-鄂霍茨克大洋板片南向俯冲作用相关的安第斯型活动大陆边缘环境,且蒙古-鄂霍茨克大洋板片在晚三叠世期间经历了低角度俯冲到高角度俯冲的转变。This paper presents zirc0n U-Pb ages,Lu-Hf isotope compositions and whole-rock geochemical data of the Late Triassic andesite from the Huolonggou area,central Great Xing＇an Range,in order to reveal the processes of southward subduction of the Mongol-Okhotsk oceanic plate.Zircons from the andesite in the Huolonggou area are euhedral to subhedral in shape,and are characterized by typical oscillatory growth zoning and high Th/U（0.48-1.47）ratios,indicating a magmatic origin.Zircon LA-ICP-MS U-Pb dating result indicates that the andesite from the Huolonggou area formed during the Late Triassic with the age of 236±1Ma.These andesite have Si O2contents of 51.44%-66.67%,total alkali（Na2O＋K2O）concentrations of 5.01%-6.88%,Al2O3contents of 13.14%-19.20%,Fe2O3-Tcontents of 5.11%-9.55%,and Ti O2contents of 0.65%-1.66%,with high MgO（2.15%-4.64%）,Cr（43.7×10^-6-212.0×10^-6）and Ni（20.2×10^-6-100.0×10^-6）contents and Mg-#values（45-55）,and belong to calc-alkaline series.The andesite samples are enriched in large ion lithophile elements（e.g.,Rb,K and Sr）and light rare earth elements,and depleted in high field strength elements（e.g.,Nb,Ta and Ti）and heavy rare earth element,with weak Eu anomalies（δEu=0.84-1.13）,similar to those of igneous rocks that form in subduction zone.Zircons of the andesite haveε（Hf）（t）values of＋8.9-＋11.6,and corresponding single-stage model（t（DM1））ages range from 525Ma to 414Ma.These characteristics suggest that the Late Triassic andesite from the Huolonggou area were derived from the partial melting of a depleted mantle wedge that had been metasomatized by subduction-related fluids,possibly with a few additions of subducting sediments,then fractional crystallization of amphibole,plagioclase and apatite occurred during magmatic evolution.Combined with regional geological data,we conclude that the Late Triassic andesite in the study area formed in an Andean-type active continental margin related to the southward subduction of the Mongol-Okhotsk

关 键 词：晚三叠世安山岩 兴蒙造山带 蒙古-鄂霍茨克洋 岩石成因 地球化学 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.144[天文地球—地质学]