内蒙古阿巴嘎旗奥陶纪岩体的发现及地质意义

Discovery of Ordovician pluton in Abaga Banner, Inner Mongolia and its geological significance

阿巴嘎旗格日敖包岩体位于贺根山断裂带北侧,为一个复式岩体,由石英闪长岩、花岗闪长岩和黑云母二长花岗岩组成,主体为二长花岗岩。采用LA--MC--ICP--MS锆石U--Pb定年方法,获得黑云母二长花岗岩206Pb/238U年龄为449±3.0 Ma,形成时代为晚奥陶世。岩石为高钾钙碱性系列,轻稀土富集,微量元素Ba、Sr、Nb、Ta、P、Ti亏损,Rb、Th、U、K、Nd、Zr等元素富集,表明其形成于活动大陆边缘环境。其形成可能与苏尼特左旗南侧俯冲事件有关。

Geri Obo complex pluton in Abaga Banner is located in northern Hegenshan fault belt,and consists of quartz diorite,granodiorite and biotite monzogranite,in which the monzogranite is the major rocks.By LA——MC——ICP——MS zircon U——Pb dating,the monzogranite 206Pb/238U age was 449±3.0 Ma,showing the Late Ordovician.Geri Obo pluton had high-K calc-alkaline characteristics,and enriched in LREE.The trace elements were depleted in Ba,Sr,Nb,Ta,P,Ti,but enriched in Rb,Th,U,K,Nd and Zr,showing Geri Obo pluton formed in active continental margins,and might be related to the subduction event in southern Sonid zuoqi.