内蒙古北山地区阿民乌素蛇绿岩的年代学、地球化学特征及大地构造意义  

Chronology,Geochemical Characteristics and Tectonic Significance of Aminwusu Ophiolite in the Beishan Area,Inner Mongolia

作　　者：孟庆涛 张正平 董洪凯 徐翠 MENG Qingtao;ZHANG Zhengping;DONG Hongkai;XU Cui(Hebei Regional Geological Survey Institute,Langfang,Hebei 065000)

机构地区：[1]河北省区域地质调查院,河北廊坊065000

出　　处：《地质与勘探》2021年第1期122-135,共14页Geology and Exploration

基　　金：中国地质调查局大兴安岭成矿带南段地质矿产调查项目《内蒙古1∶5万标山、咸味井、骨头井、化石山幅区域地质矿产调查》(编号:12120113056000)资助。

摘　　要：内蒙古北山地区阿民乌素蛇绿岩是芨芨台子-小黄山蛇绿岩带的重要组成部分,主要由变质辉长岩和极少强蛇纹石化橄榄岩组成。变质辉长岩LA-ICP-MS锆石U-Pb年龄453±12 Ma,形成于晚奥陶世。强蛇纹石化橄榄岩MgO(36.90%~37.44%)、Ni(1980×10^-6~2232×10^-6)、Cr(2312×10^-6~2506×10^-6)含量高,而Al2O3(0.59%~1.41%)、TiO 2(0.01%~0.02%)和∑REE(0.85×10^-6~3.25×10^-6)含量低,具亏损地幔岩特征;变质辉长岩MgO(7.22.20%~11.66%)相对含量高;Al2O3(15.61%~18.79%)、TiO 2(0.20%~0.29%)、P2O5(0.01%)、K2O+Na2O(1.36%~2.43%)含量低,且K2O<Na2O;∑REE(12.32×10^-6~17.44×10^-6)相对较高,轻稀土弱亏损,Eu正异常明显,具向左缓倾型稀土配分模式,与N-MORB类似;富集Rb、Ba、Sr等大离子亲石元素,亏损Nb、P、Zr等高场强元素,具俯冲消减带(SSZ型)蛇绿岩地球化学特征。综合大地构造位置、区域地质、岩石组合及地球化学特征分析认为:阿民乌素蛇绿岩形成于弧后扩张环境,为早古生代白云山-洗肠井古亚洲洋向北俯冲,引起弧后扩张所致。The Aminwusu ophiolite in the Beishan area,Inner Mongolia is an important part of the Jijitaizi-Xiaohuangshan ophiolite mélange belt.This rock consists of metamorphic gabbro and little serpentinized peridotite.LA-ICP-MS zircon U-Pb dating of metamorphic gabbro shows that the metamorphic gabbro formed at 453±12 Ma,i.e.,in Late Ordovician.The content of MgO(36.90%~37.44%),Ni(1980×10^-6~2232×10^-6),and Cr(2312×10^-6~2506×10^-6)in serpentinized peridotite is relative high,and the content of Al 2 O 3(0.59%~1.41%),TiO2(0.01%~0.02%)and REE(0.85×10^-6~3.25×10^-6)is relative low,showing the feature of depleted mantle.The content of MgO(7.22.20%~11.66%)in metamorphic gabbro is relative high,that of TiO 2(0.20%~0.29%),P2O5(0.01%),K2O+Na2O(1.36%~2.43%,K 2 O<Na 2 O)is low.It has a relatively high∑REE(12.32×10^-6~17.44×10^-6),in which the LREE is weakly depleted with positive Eu anomalies.Chondrite-normalized REE patterns have a left-inclined feature,similar to N-MORB.The primitive mantle normalized trace element patterns are characterized by the enrichment of the LILE(Rb,Ba and Sr)and depletion of the HFSE(Nb,P and Zr),implying features of supra-subduction zone(SSZ)type ophiolite.Combined with the tectonic setting of the ophiolite,field observations,the rock association and the analysis of geochemistry,this work suggests that the Aminwusu ophiolite formed in the tectonic environment of a back-arc expansion,resulting from northward subduction of the Paleo-Asian ocean around Baiyunshan-Xichangjing in Early Paleozoic.

关 键 词：蛇绿岩 地球化学 弧后扩张 阿民乌素 北山地区 内蒙古 

分 类 号：P59[天文地球—地球化学]