摘要
海南岛东北缘木兰头地区发现的榴辉岩为约束古特提斯洋在东南亚地区的构造演化过程提供了重要的研究对象。全岩Sm-Nd等时线年龄将木兰头榴辉岩原岩的形成时代重新限定为389.6±9.1Ma的中泥盆世,与哀牢山-马江缝合带蛇绿混杂岩的初始形成时间一致。榴辉岩主体呈现轻稀土元素亏损,具有较为明显的Ce负异常,大离子亲石元素略微亏损和Nb、Ta元素的轻微负异常;具有相对较为亏损的Sr-Nd同位素组成,I_(Sr)=0.705~0.707,ε_(Nd)(t)=+0.8~+6.0,表现出典型的洋中脊玄武岩地球化学特征,表明在中泥盆世390~380Ma沿金沙江-哀牢山-马江和海南岛北缘分布有连续的东古特提斯洋大洋中脊。仅少量样品表现出轻稀土元素轻微富集,具有轻微的Eu负异常,中等富集大离子亲石元素,且表现出明显的Nb、Ta元素正异常,代表了俯冲碰撞过程中俯冲沉积物和变质洋壳组分交代作用的结果。自石炭纪340~330Ma以来,大洋板片沿海南岛北缘向海南岛地块俯冲,由此形成了木兰头榴辉岩的进变质作用和邦溪-晨星沿线分布的弧后盆地。因此,哀牢山-马江缝合线应向东延伸至海南岛东北缘木兰头附近。
The occurrence of eclogite in the Mulantou area along the northeastern margin of the Hainan Island provides valuable insights into the tectonic evolution of the paleo-Tethys Ocean in southeastern Asia.Whole-rock Sm-Nd isochron analysis yields a formation age of its protolith at 389.6±9.1Ma,the Middle Devonian,which is consistent with the formation age of the ophiolite mélange along the Ailaoshan-Song Ma suture zone.The eclogite generally displays LREE-depleted patterns,a negative Ce anomaly,slightly low LILE concentrations,and minor negative Nb and Ta anomalies.It also shows depleted Sr-Nd isotopic compositions with I Sr=0.705-0.707 andε_(Nd)(t)=+0.8-+6.0.Therefore,the eclogite in the Mulantou area mainly consists of normal mid-oceanic ridge basalt,indicating that there was a continuous eastern oceanic ridge of the eastern Paleo-Tethys Ocean along the Jinshajiang-Ailaoshan-Song Ma suture and the northeastern margin of the Hainan Island during the Middle Devonian.Only a few samples show moderately LREE-rich patterns,a minor negative Eu anomaly,moderately high LILE,and positive Nb and Ta anomalies,which result from the metasomatism of metamorphic sediments and oceanic crust during subduction.From 340Ma to 330Ma,during the Carboniferous,the oceanic slab subducted southward beneath the Hainan Island,leading to the prograde metamorphism of the Mulantou eclogite and the formation of the back-arc basin along the Bangxi-Chenxing area.Therefore,the Ailaoshan-Song Ma suture should extend eastward to the Mulantou area along the northeastern margin of the Hainan Island.
作者
郑勇
林弟
ZHENG Yong;LIN Di(Key Laboratory of Continental Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Jiangsu Donghai Continental Deep Hole Crustal Activity National Observation and Research Station,Donghai 222300,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China;Hainan Key Laboratory of Marine Geological Resources and Environment,Haikou 570206,China;Hainan Provincial Institute of Geological Survey,Haikou 570206,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2024年第12期3861-3875,共15页
Acta Petrologica Sinica
基金
中国地质科学院基本科研业务费项目(JKYQN202314)
中国地质调查局地质调查项目(DD20221630)联合资助。
关键词
海南岛
榴辉岩
东古特提斯洋
俯冲碰撞
缝合线
Hainan Island
Eclogite
Eastern Paleo-Tethys Ocean
Subduction
Suture
作者简介
第一作者:郑勇,男,1984年生,博士,副研究员,构造地质学专业,E-mail:zygeology@163.com。
