中亚造山带中段南缘圆包山组碎屑锆石U-Pb年龄、物源及其构造演化意义

摘要

取自圆包山组砂岩样品中的碎屑锆石作LA-ICP-MS U Pb定年,获得两个数据年龄区间:409～431Ma(峰值420Ma)和458～488Ma(峰值488Ma).圆包山组底部发育的笔石化石和420Ma的锆石峰值年龄将圆包山组的时代限定为早志留世后,通过与兴蒙造山带的构造演化对比,认为圆包山组时代为早志留世至早泥盆世.对圆包山组中发育的沉积构造进行古流向分析,认为圆包山组物源区位于杭乌拉北西方向.结合区域岩浆演化资料分析,圆包山组物源区为呼和套尔盖地区.在圆包山组中还检测到继承锆石,新元古代分布于559～952Ma,中元古代分布于1011～1460Ma,古元古代分布于1629～2490Ma.从前人对西伯利亚板块南部、塔里木板块以及南蒙古微板块的相关锆石年龄结果总结发现,华北板块与周围板块最主要的区别在于没有或者很少有中元古代晚期至新元古代早期的锆石年龄记录,阿拉善地块也缺少1.0～1.2Ga锆石年龄记录.综上,认为研究区在古生代构造位置属于南蒙古微板块南部的一部分,元古代物源来自塔里木板块.另外由碎屑锆石年龄在地层中分布特征来看,研究区在早泥盆世后隆升作用明显,构造活动性增强,受到塔里木板块影响逐渐加强.%LA-ICP-MS dating of detrital zircons from the Yangbaoshan Formation sandstone samples yielded two ages of 409～431Ma (peaking 420 Ma) and 458～488Ma (peaking 488 Ma).Graptolite found at the bottom of the Yuanbaoshan Formation and the zircon with a peaking age of 420 Ma constrain the time of the Yuanbaoshan Formation within the Early Silurian,and comparison study with the tectonic evolution of the Xing-Meng orogenic belt indicates that the age of Yuanbaoshan Formation should be he Early Silurian to Middle Devonian.The analysis of paleocurrent direction of the sedimentary structures in the Yuanbaoshan Formation also shows that the provenance area is located in the northwest.And the provenance area may be the Huhetaoergai area according to the previous research results about the age of magmatic rocks.The study reveals three generations of Proterozoic zircons:Neoproterozoic (559Ma and 952Ma),Mesoproterozoic (from 1011Ma to 1460Ma) and Paleoproterozoic (from 1629Ma to 2490Ma).Based on the summary of zircon ages in the southern Siberian block,the Tarim block and the southern Mongolia microplate,it can be concluded that the main difference between the North China plate and the surrounding plate is that there is no or less records of late Mesoproterozoic to early Neoproterozoic zircon age,and the Alxa block is lack of the zircon age record of 1.0 ～ 1.2Ga in this study area.Therefore,it can be considered that the study area tectonically belonged to the southern part of the southern Mongolia microplate in the Paleozoic,and the provenance in this period derived from the Tarim craton.In addition,based on the distribution characteristics of detrital zircon age in the strata,the study area was characterized by obvious uplift and strong tectonic activity after the early Devonian,indicating that the study area was affected increasingly by the Tarim Plate.