内蒙古伊敏地区下石炭统红水泉组砂岩物源分析及其构造意义

Provenance analysis and its tectonic significance of Lower Carboniferous Hongshuiquan Formation sandstone in Yimin area of Inner Mongolia

碎屑沉积物成份与源区构造环境、构造背景及源区岩石性质密切相关。通过对伊敏地区红水泉组砂岩样品进行砂岩碎屑颗粒成分统计、地球化学特征及碎屑锆石LA-ICP-MS U-Pb年代学等物源分析方法,确定红水泉组砂岩为长石岩屑砂岩,物源区构造背景主要为大陆岛弧环境,其物源类型为切割型岛弧。红水泉组砂岩中最年轻的碎屑锆石年龄为338±3 Ma,该年龄值表明红水泉组形成的时代为早石炭世密西西比中期的韦宪阶或之后。903～1 676 Ma的分散元古界锆石年龄和～780 Ma新元古代锆石年龄峰值,可能反映南蒙古微板块基底年龄信息。～500 Ma和～380 Ma的年龄峰值指示源区可能经历了多期岩浆事件:～500 Ma的岩浆锆石物源可能来自额尔古纳与兴安地块闭合相关的后造山花岗岩,～500 Ma的变质锆石可能来自变质基底,～380 Ma的物源可能反映额尔古纳—兴安地块与松嫩地块至少在晚泥盆世开始碰撞拼贴,并导致该区存在一个晚泥盆世—早石炭世的岩浆弧。

Through the study of sandstone detrital component statistics,geochemical characteristic and detrital zircon LA—ICP—MS U—Pb dating of Hongshuiquan Formation sandstone in Yimin area,the authors confirm that the sandstone lithology of Hongshuiquan Formation is feldspar lithic sandstone in category,the tectonic setting of source area is continental island arc in Paleo environment,and the provenance is divided island arc in type.The youngest dating of detrital zircon of Hongshuiquan Formation sandstone is 338±3 Ma,which indicates the formation as the Visean of Middle Mississippian in Carboniferous in age even younger.The Proterozoic zircon aged in 903～1 676 Ma and the New Proterozoic zircon peak may aged in ～780 Ma,reflect the basement age of southern Mongolian micro-block.The peak age of ～500 Ma and ～380 Ma indicate that the material source area probably went through multi-staged magma events,in which the ～500 Ma indicates the source might come from post-orogenic granites concern with the closure of Erguna and Xing＇an blocks,while the ～380 Ma may reflect that the Erguna—Xing＇an block started to collide and collage with Songnen block at Late Devonian,at least,and formed a magmatic arc during the Late Devonian—Early Carboniferous.