内蒙古乌拉特中旗索伦山地区中元古代石英闪长岩的发现及其构造意义

Discovery of the Mesoproterozoic Quartz Diorite in the Solonker Area,Urad Zhong Qi,Inner Mongolia,and its Tectonic Significance

在内蒙古乌拉特中旗索伦山地区首次发现了中元古代的石英闪长岩岩体。岩石富镁、碱(尤其富钠)和钙,贫硅、钛,属碱性系列岩石。轻稀土富集,重稀土相对亏损,Eu异常不明显。微量元素富集Rb、Ba、Sr等大离子亲石元素,亏损Nb、Ta、Zr、Hf、Ti等高场强元素,显示出与板块俯冲作用有关的弧岩浆特点。岩体形成于与俯冲消减作用有关的火山弧构造环境,其岩浆来源于受俯冲的板片流体/沉积物交代的岩石圈地幔部分熔融,源岩可能为变质玄武岩或变质英云闪长岩。采用LA-ICP-MS锆石U-Pb法获得的207 Pb/206 Pb加权平均年龄为1410±11Ma,代表了该石英闪长岩体的结晶年龄。结合区域地质背景,认为至少在1410Ma时华北北缘发生了板块俯冲汇聚作用,石英闪长岩可能是板块俯冲汇聚作用的直接产物。该成果为华北板块北缘俯冲汇聚作用开始的时限提供了新证据,同时为华北板块北缘在中元古代构造演化提供了重要依据。

Mesoproterozoic quartz diorite was discovered for the first time in the Solonker area,Urad Zhong Qi,Inner Mongolia.The quartz diorite is rich in Mg,alkali（especially Na）,and Ca,and poor in Si and Ti,suggesting it should belong to alkaline rocks series.The rock is enriched in LREE and depleted in HREE and shows no obvious Eu anomaly.Trace elements analysis shows that the rocks are rich in LILE（Rb,Ba and Sr）and poor in HFSE（Nb,Ta,Zr,Hf and Ti）,indicating the signature of arc magma related plate subduction.The diorite probably formed in a volcanic arc setting,with magma deriving from partial melting of the mantle wedge metasomatized by subducted slab-released fluids/melts and source rocks likely being metabasaltic and metatonalite rocks.LA-ICP-MS zircon U-Pb dating yields a weighted 207 Pb/206 Pb average age of 1410±11 Ma,which likely represents the crystallization age of the quartz diorite.Combined with the regional tectonic setting,this study concludes that the northern and northwestern margins of North China Plate experienced the convergence of plate subduction at least at 1410 Ma,indicating that the quartz diorite was the direct product of the plate subduction.The results in this study provide new evidence for the start time of northward subduction convergence of the northern margin of North China Plate and are the important basis for tectonic evolution of northern North China in the Mesoproterozoic.