大兴安岭南段兴-蒙草原区二叠纪砂岩物源分析

A provenance analysis of Permian sandstones in southern Da Hinggan Mountains-Inner Mongolia steppe zone

对大兴安岭南部兴-蒙草原区二叠纪砂岩的统计研究表明,本区二叠纪砂岩主要为长石岩屑砂岩,大量非成熟组分为该区二叠纪砂岩的形成提供了物源。主量、微量和稀土元素特征指示,二叠纪砂岩物源区的构造背景主要为大陆岛弧环境,砂岩碎屑来自上地壳长英质源区。二叠纪砂岩的时代由老到新表现出由再旋回造山带向切割岩浆弧源区过渡的特征。结合沉积学特征,反映中、晚二叠世构造背景由活动陆缘逐渐趋于稳定,该时期记录了中亚造山带东段最终闭合的过程。

Petrographic study and Dickison＇s framework component statistical analysis show that the Permian sandstones are mainly feldspathic litharenite,and the debris was mainly derived from immature components.The data of major elements,minor elements and rare earth elements indicate that the tectonic setting of the provenance was continental island arc,with the sandstone debris mainly derived from upper crustal felsic rocks.The Permian sandstones,from old to young,are characterized by transition from recycled orogenic belt to magmatic provenance.In combination with petrological studies,the authors hold that the tectonic setting of the Permian sandstones tended gradually to become stable,which recorded the final closure process in the eastern part of the central Asian orogenic belt.