内蒙古白乃庙地区白音都西群的碎屑锆石年龄及其构造意义  

Zircon Dating of the Baiyinduxi Group in Inner Mongolia and Its Tectonic Interpretation

作　　者：谷丛楠[1] 周志广[1] 张有宽 柳长峰[1] 刘文灿[1] 於炀森[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]内蒙古地质调查研究院,内蒙古呼和浩特010020

出　　处：《现代地质》2012年第1期1-9,共9页Geoscience

基　　金：国土资源部中国地质调查局"华北地区基础地质及数据更新"项目(1212010811001);中国地质调查局"东北地区基础地质调查及数据更新"项目(1212010881207);中国地质调查局"中蒙边境成矿带地质-地球物理综合剖面研究"项目(1212010070505)

摘　　要：白音都西群是内蒙古中部白乃庙岛弧带以北和温都尔庙杂岩以南发育的一套中级变质岩系,为确定白音都西群的地层时代,笔者于稳定的白音都西群地层采集了两块新鲜的变质石英砂岩样品,共进行了100粒碎屑锆石LA-MC-ICP-MS测年。两件样品的锆石特征具相似性,指示其原岩主要是由同期或略早期的岩浆岩风化后就近沉积的产物。所有锆石的206Pb/238U表面年龄介于518～294 Ma之间,与华北板块北缘的古生代弧岩浆岩锆石年龄非常吻合,表明该区古生代弧岩浆岩是白音都西群的主要沉积源区。因此,白音都西群的原岩可能是一套弧前沉积建造,其形成时间应该是伴随着古亚洲洋的俯冲消减和古生代弧岩浆作用的整个过程,其后在碰撞造山过程中发生了变形和变质作用。由于白音都西群被晚二叠世未变形花岗岩(254 Ma)侵入,表明其原岩最终形成到发生变形变质作用应当介于294～254 Ma之间。故推测沿着索伦缝合带的碰撞缝合作用可能发生在早—中二叠世。A set of medium metamorphic clasolite exposing in the area,sandwiched by the Bainaimiao arc magmatic and Wenduermiao complex rock zones in the middle Inner Mongolia,is known as the Baiyinduxi Group.Analysis of zircon（detrital grains） by using LA-MC-ICP-MS,sampled from the quartzsand stone of the group indicates that the apparent age is dated by 206Pb/238U technique,ranging from 294 Ma to 518 Ma and coinciding with the zircon dating from the Paleozoic arc magmatite of the northern margin of the North China block.It is suggested that the Paleozoic arc magmatite might be a sediment-source of the Baiyinduxi Group.Protolith of the group is likely a set of forearc depositional sequence,forming throughout the process of both the subduction of the Paleo-Asian Ocean floor and the Paleozoic magmatism,and was undergone with deformation and metamorphism due to orogenesis.Furthermore,obvious characters of the zircon samples showing magma genesis indicate that the protolith would be weathered sediments of either contemporaneous or slightly early magmatites.In addition,the fact that the Baiyinduxi Group was intruded by the end-Permian granites suggests that the forming,deformation and metamorphism of the protolith should take place in the period from 294 Ma to 254 Ma.Therefore,a collision along the Solonker suture zone should occur in the Early and Middle Permian.

关 键 词：碎屑锆石测年 白音都西群 索伦缝合带 内蒙古 

分 类 号：P534.46[天文地球—古生物学与地层学] P597[天文地球—地质学]