内蒙古沙巴尔吐地区中二叠世蛇绿构造混杂岩及同期花岗质杂岩的发现及地质意义  

The discovery and tectonic implications of Middle Permian ophiolite melange and coeval granitic complex in the Shabaetu area,Inner Mongolia

作　　者：李英雷 武广[1] 贺宏云[3] 陈公正 杨飞 李铁刚 宋广超 肖剑伟[3] LI Ying-lei;WU Guang;HE Hong-yun;CHEN Gong-zheng;YANG Fei;LI Tie-gang;SONG Guang-chao;XIAO Jian-wei(Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth and Space Sciences,Peking University,100871 Beijing,China;Inner Mongolia Key Laboratory of Magmatic Mineralization and Ore-Prospecting,Geological Survey Institute of Inner Mongolia,Hohhot 010020,China;No.3 Institute of Geological Exploration,Inner Mongolia Bureau of Geology and Mineral Resources,Hohhot 010010,China)

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871 [3]内蒙古自治区岩浆活动成矿与找矿重点实验室内蒙古自治区地质调查院,内蒙古呼和浩特010020 [4]内蒙古第三地质矿产勘查开发有限责任公司,内蒙古呼和浩特010010

出　　处：《岩石矿物学杂志》2021年第2期217-235,共19页Acta Petrologica et Mineralogica

基　　金：科技部深地专项(2017YFC0601303);国家自然科学基金资助项目(4190021252);中国地质调查局项目(DD20160048-09)。

摘　　要：中亚造山带东段内蒙古兴安盟扎赉特旗地区作为二连-贺根山断裂的东延部分,蕴含了古亚洲洋俯冲消亡过程及洋-陆转换的关键信息,然而对于该区蛇绿构造混杂岩的研究相对薄弱,成为制约古亚洲洋构造演化研究的瓶颈。本文在扎赉特旗沙巴尔吐地区发现了蛇绿构造混杂岩、与岛弧环境相关的英云闪长岩-奥长花岗岩和碱长花岗岩组合。对蛇绿构造混杂岩中超镁铁质岩和碱长花岗岩开展LA-ICP-MS锆石U-Pb测年显示其年龄分别为279.2±3.3 Ma和278.2±1.7 Ma,表明其形成于中二叠世早期。超镁铁质岩含有低的SiO2含量(43.54%~46.38%),低Na_(2)O和K_(2)O而富MgO,Mg#为89~94,显示亏损地幔-过渡型地幔特征,起源于约70%的石榴石二辉橄榄岩的部分熔融,属俯冲型(SSZ)蛇绿岩。英云闪长岩-奥长花岗岩属准铝质钙碱性系列,高Al2O3含量,相对富钠贫钾,高Sr(平均600.00×10^(-6))、低Y(平均12.50×10^(-6))和Yb(平均1.18×10^(-6)),具典型。型埃达克岩特征,是俯冲环境下低钾洋壳玄武岩部分熔融的产物。碱长花岗岩富硅和碱,低铁和镁,具有高的正εHf(t)值(平均+18.9),位于亏损地幔线之上,一阶段、二阶段模式年龄基本近于或者小于岩石结晶年龄,起源于岛弧型的新生地壳。沙巴尔吐蛇绿构造混杂岩代表中二叠世早期洋内俯冲的产物,表明古亚洲洋在中二叠世早期未闭合,仍存在持续性的俯冲活动,闭合时间至少应在中二叠世之后。Located in the eastern part of the Central Asian Orogenic Belt,the Jalaid Banner of Inner Mongolia is considered to be controlled by the eastern extension of Erlian-Hegenshan fault.It contains the key information of the subduction and extinction process of the Paleo-Asian Ocean.However,the studies of the Ophiolite melange in this area are relatively weak.In this study,the ophiolite melange,tonalites-trondhjemite and alkali feldspar granite assemblages related to island arc environment were found in Shabaertu region.Zircon U-Pb dating of the ophiolite melange shows that their ages are 279.2±3.3 Ma and 278.2±1.7 Ma,respectively,indicating their emplacement in Early Permian.The ultramafic rocks have low SiO2 content(43.54%~46.38%),low Na_(2) O and K_(2) O values,but rich MgO,with Mg#of 89~94,showing the features of depleted mantle-transitional mantle,which originated from about 70%partial melting of garnet lherzolite.They belong to the supra-subduction zone type(SSZ).The tonalite-trondhjemite is a typical O-type adakite and belongs to the metaluminous and calc-alkaline series,relatively rich in Al2 O3 and Sr(averaging 600.00×10^(-6)),but low in Y(averaging 12.50×10^(-6))and Yb(averaging 1.18×10^(-6)),suggesting that they originated from partial melting of the low-K oceanic crust basalts in subduction environment.The alkali feldspar granites are rich in silicon and alkali and low in iron and magnesium.They have high positiveεHf(t)values(averaging+18.9)and are located above the depleted mantle line,with the in-situ zircon Hf isotope one-stage and twostage model age equal to or less than the crystallization ages of rocks,so they might have been derived from the island arc type juvenile crust.The Shabaetu ophiolite melange represents the product of intra-oceanic subduction in the early Middle Permian,implying that the Paleo-Asian Ocean was not closed in the early Middle Permian,and the closure time should be at least after the Middle Permian.

关 键 词：中亚造山带 大兴安岭 中二叠世 蛇绿构造混杂岩 花岗质杂岩 古亚洲洋 

分 类 号：P588.12[天文地球—岩石学]