古太平洋板片晚二叠-早三叠世俯冲后撤:来自海南岛弧岩浆作用的制约  

Late Permian to Early Triassic subduction and retreating of the Paleopacific slab: Constraints from continental arc magmatism in Hainan Island

作　　者：刘飞[1,2,3,4] 杨经绥 冯光英[1,3] 牛晓露 李观龙[1] 张超凡 LIU Fei;YANG JingSui;FENG GuangYing;NIU XiaoLu;LI GuanLong;ZHANG ChaoFan(Key Laboratory of Deep Earth Dynamics of MNR,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Shandong Academician Workstation of Diamond Mineralization Mechanism and Exploration,Shandong No.7 Exploration Institute of Geology and Mineral Resources,Linyi 276006,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)

机构地区：[1]自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100037 [2]山东省金刚石成矿机理与探测院士工作站,山东省第七地质矿产勘查院,临沂276006 [3]南方海洋科学与工程广东省实验室(广州),广州511458 [4]地质过程与矿产资源国家重点实验室,中国地质大学,北京100083 [5]南京大学地球科学与工程学院,南京210023

出　　处：《岩石学报》2022年第11期3455-3483,共29页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(92062215);中国地质调查局地质调查项目(DD20221630、D20221817);山东省地质矿产勘查开发局第七地质大队科研项目(QDKY202007);深地动力学国家重点实验室自主课题(J1901-32);地质过程与矿产资源国家重点实验室课题(GPMR202115);南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(GML2019ZD0201)联合资助.

摘　　要：海南岛大规模二叠-三叠纪侵入岩的形成是与古特提斯洋有关,还是与古太平洋俯冲闭合有关还存在巨大争议。本文对琼中金波两处辉绿岩脉及其围岩花岗岩的研究显示,露头1辉绿岩脉的锆石U-Pb年龄为245.4±3.8Ma,TiO_(2)含量(1.07%~1.18%)低,而MgO(8.60%~9.41%)和Mg^(#)值(62.31~65.02)较高,为钙碱性系列,球粒陨石和原始地幔标准化配分曲线中具有明显的Eu、Nb、Ta、Ti和Ba负异常,以及显著Th、U、Zr、Rb和Pb等正异常,(^(87)Sr/^(86)Sr)_(i)=0.707138~0.712797,(^(143) Nd/^(144)Nd)_(i)=0.511884~0.511965,ε_(Nd)(t)值为-7.01~-8.58,指示其形成于大陆岛弧环境。相比之下,露头2辉绿岩锆石U-Pb年龄为242.8±3.1Ma,但其TiO_(2)(2.65%~3.06%)含量较高,而MgO(4.24%~5.39%)和Mg^(#)值(40.09~45.86)较低,具有Eu、Rb、Pb、Nb、Ta和Ti弱正异常和Th负异常,(^(87)Sr/^(86)Sr)_(i)=0.690244~0.717031,(^(143) Nd/^(144)Nd)_(i)=0.512886~0.512915,ε_(Nd)(t)值为+6.41~+7.93,具有板内玄武岩的特征,指示其形成于板内裂解环境。辉绿岩脉围岩二长花岗岩的锆石U-Pb年龄为255.3±3.0Ma和255.7±3.2Ma,含少量角闪石和黑云母,具有较高的SiO_(2)(71.62%~73.72%)、Na_(2)O+K_(2)O(6.60%~9.17%)和Al_(2)O_(3)(平均14.88%)含量,A/CNK值(0.97~1.03)较低,亏损Nb、Ta、Ti、Sr和Ba,富集Rb、Th、U和Pb,为高分异I型岛弧花岗岩。总的来看,二长花岗岩和辉绿岩形成于大陆岛弧挤压向伸展过渡的构造环境。对比二叠-三叠纪侵入岩体的走向、碰撞前-同碰撞-碰撞后岩浆岩的时代以及榴辉岩的变质年龄等,发现海南岛侵入岩与哀牢山-松马造山带明显不同,而与日本和朝鲜半岛的岛弧岩浆岩类似,由此我们认为海南岛大规模晚二叠-早三叠世岩浆岩为古太平洋板片向欧亚板块俯冲后撤的产物,后撤过程受到古特提斯俯冲板片的影响。It is still controversial whether the formation of Permian-Triassic intrusive rocks in Hainan Island is related to subduction and closure of the Paleo-Tethys Ocean or the Paleo-Pacific Ocean.Zircon U-Pb age of dolerite dike in the first outcrop is 245.4±3.8Ma,the whole-rock geochemical contents of dolerites are characterized by low TiO_(2)(1.07%~1.18%),and high MgO contents(8.60%~9.41%)and high Mg^(#)value of 62.31~65.02,showing a calc-alkaline series.The chondrite-and primitive mantle-normalized diagrams display obvious negative anomalies of Eu,Nb,Ta,Ti and Ba,and significant positive anomalies of Th,U,Zr,Rb and Pb.The(^(87)Sr/^(86)Sr)_(i) values range from 0.707138 to 0.712797,(^(143) Nd/^(144)Nd)_(i) values range from 0.511884 to 0.511965,ε_(Nd)(t)values(-7.01~-8.58)are extremely low,indicating that they were formed in a continental island arc environment.In contrast,the U-Pb age of dolerite dikes in the second outcrop is 242.8±3.1Ma,their whole-rock,however,geochemical contents are differently characterized by high contents of TiO_(2)(2.65%~3.06%),low values of MgO(4.24%~5.39%)and Mg^(#)(40.09~45.86),and weak positive anomalies of Eu,Rb,Pb,Nb,Ta and Ti and negative anomalies of Th in the chondrite-and primitive mantle-normalized diagrams,and showing the typical features of intraplate basalts.The(^(87)Sr/^(86)Sr)i values range from 0.690244 to 0.717031,(^(143) Nd/^(144)Nd)_(i) values range from 0.512886 to 0.512915,ε_(Nd)(t)values are slightly high,from+6.41 to+7.93,indicating that they were formed in an intraplate extensional environment.Two zircon U-Pb ages of the wall-rock monzogranites of dolerite dike in the first outcrop are 255.3±3.0Ma and 255.7±3.2Ma,respectively.They are characterized by minor components of amphibole and biotite,high contents of SiO_(2)(71.62%~73.72%),Na_(2)O+K_(2)O(6.60%~9.17%)and Al_(2)O_(3)(average 14.88%),but low A/CNK values of 0.97~1.03.There are obvious negative anomalies of Nb,Ta,Ti,Sr and Ba,and positive anomalies of Rb,Th,U and Pb in the chondrite-and primitive mantle-

关 键 词：二叠-三叠纪 二长花岗岩 辉绿岩 俯冲后撤 大陆岛弧 古太平洋 海南岛 

分 类 号：P588.121[天文地球—岩石学] P588.124[天文地球—地质学] P597.3