| 额尔古纳地块早-中三叠世安山岩的发现及其对蒙古-鄂霍茨克洋南向俯冲的指示 |
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| 引用本文： | 李强,程学芹,陈伟,刘洪章,张涛,张建珍,贾立民,杨宁,刘腾飞.额尔古纳地块早-中三叠世安山岩的发现及其对蒙古-鄂霍茨克洋南向俯冲的指示[J].地球科学,2021,46(8):2768-2785. |
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| 作者姓名： | 李强 程学芹 陈伟 刘洪章 张涛 张建珍 贾立民 杨宁 刘腾飞 |
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| 作者单位： | 1.河北省区域地质调查院, 河北廊坊 065000 |
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| 基金项目： | 中国地质调查局地质矿产调查项目12120115032001国家自然科学基金项目41902099 |
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| 摘 要： | 安山岩与俯冲构造环境密切相关，对安山岩的研究可以获得俯冲作用发生时代及相关俯冲过程的重要信息.报道了大兴安岭北段、额尔古纳地块之上凤水山地区早-中三叠世安山岩的岩石学特征、锆石U-Pb年龄以及全岩地球化学数据，以揭示该地区蒙古-鄂霍茨克大洋板片南向俯冲作用的初始过程.凤水山地区安山岩的锆石多数呈自形-半自形短柱状、粒状，具有典型的震荡生长环带和高Th/U（0.23~1.34）比值，暗示其为岩浆成因锆石.锆石LA-MC-ICP-MS U-Pb同位素测年结果显示其分别形成于251±2 Ma和243±2 Ma，分属早三叠世和中三叠世，表明凤水山地区存在早中生代安山岩.这些早中生代安山岩的SiO2含量介于53.52%~60.38%，Al2O3含量介于16.17%~17.41%，Fe2O3T含量为5.55%~8.93%，MgO含量介于1.96%~5.97%，TiO2含量介于0.97%~1.67%，全碱（K2O+Na2O）含量为5.60%~8.05%，Na2O/K2O比值为1.23~2.51，铝饱和指数A/CNK介于0.86~0.97，具有较高的Mg#值（47~75），为钙碱性系列岩石.岩石样品富集Rb、Ba、U、K、Pb等大离子亲石元素和轻稀土元素，明显亏损Nb、Ta、Ti、P等高场强元素和重稀土元素，具有微弱的负Eu异常（δEu=0.74~0.99），与俯冲带大陆边缘弧岩浆岩地球化学特征类似.凤水山地区早中生代安山岩岩浆可能起源于幔源玄武质岩浆与壳源硅质熔体的混合作用，而幔源玄武质岩浆起源于俯冲板片沉积物或沉积物熔体改造的富集地幔，可能与前人提出的MASH（melting，assimilation，storage and homogenization）过程一致.因此，研究区三叠纪安山岩形成于蒙古-鄂霍茨克大洋板片南向俯冲相关的安第斯型活动大陆边缘环境.
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| 关 键 词： | 大兴安岭北段 额尔古纳地块 早-中三叠世安山岩 锆石U-Pb年龄 蒙古-鄂霍茨克洋 岩石成因 地质年代学 地球化学 |
| 收稿时间： | 2020-08-15 |
Discovery of Early-Middle Triassic Andesite in Erguna Massif and Its Indication of Southward Subduction of Mongol-Okhotsk Ocean Plate |
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| Li Qiang,Cheng Xueqin,Chen Wei,Liu Hongzhang,Zhang Tao,Zhang Jianzhen,Jia Limin,Yang Ning,Liu Tengfei.Discovery of Early-Middle Triassic Andesite in Erguna Massif and Its Indication of Southward Subduction of Mongol-Okhotsk Ocean Plate[J].Earth Science-Journal of China University of Geosciences,2021,46(8):2768-2785. |
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| Authors: | Li Qiang Cheng Xueqin Chen Wei Liu Hongzhang Zhang Tao Zhang Jianzhen Jia Limin Yang Ning Liu Tengfei |
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| Abstract: | The andesite is closely related to the subduction tectonic environment,and the study of andesite can obtain important information about the age of subduction and related subduction processes. In this paper it presents petrographic characteristics,whole-rock geochemical data and zircon U-Pb ages of the Early to Middle Triassic andesites from the Fengshui Mountain area in the Erguna massif in the northern Great Xing'an Range for the purpose of revealing the initial southward subduction of the Mongol-Okhotsk oceanic plate. Most of the zircons from the andesite in the Fengshui Mountain area are euhedral to subhedral in shape,with typical oscillating growth zonation and relatively high Th/U ratios (0.23-1.34),indicative of magmatic zircons. Zircon LA-ICP-MS U-Pb dating yields two ages of 251±2 Ma and 243±2 Ma for andesite in the Fengshui Mountain area,indicative of Early and Middle Triassic ages for the andesites. These Early Mesozoic andesites have typical geochemical characteristics of active continental margin arc magmatite with SiO2,Al2O3,K2O,Na2O,Fe2O3T,MgO,TiO2 and total alkali (K2O+Na2O) contents ranging from 53.52% to 60.38%,16.17% to 17.41%,1.60% to 4.60%,3.83% to 4.65%,5.55% to 8.93%,1.96% to 5.97%,0.97% to 1.67%,and 5.60% to 8.05%,respectively. These andesites are high K calc-alkaline with Na2O/K2O ratios ranging from 1.23 to 2.51,A/CNK values (aluminum saturation index) from 0.86 to 0.97 and Mg# values ranging from 47 to 75. These volcanic rocks are enriched in large ionic lithophile elements such as Rb,Ba,U,K,Pb and light rare earth elements,but depleted in high field strength elements such as Nb,Ta,Ti,P and heavy rare earth elements,with weak negative Eu anomaly (δEu=0.74-0.99). These Early Mesozoic andesitic rocks are geochemically similar to the typical andesites in Andean,thus indicating that they are most likely formed in the Andean-type active continental margin environment related to the southward subduction of the Mongol-Okhotsk oceanic plate. |
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