内蒙古巴林右旗林西组粉砂岩碎屑锆石U-Pb年龄及其对古亚洲洋最终闭合的制约

为探究出露于内蒙古巴林右旗西拉木伦河以北地区的碎屑岩的形成时代和构造背景，对碎屑岩组合中的粉砂岩样品进行了LA-ICP-MS锆石U-Pb同位素测年，结果显示，98颗锆石的谐和年龄主要集中分布在5个年龄区间，分别为252~315 Ma、376~523 Ma、752~1097 Ma、1465~1694 Ma、1833~2563 Ma。最年轻的一组锆石年龄为252 Ma，该年龄值限定了该组地层的沉积下限年龄为晚二叠世。锆石年龄频谱图可以反映出该地层具有多物源供给的特点，既有中亚造山带南缘的年龄信息，又具有华北克拉通北缘老基底的年龄信息，表明本地区的林西组沉积物源主要来自中亚造山带南缘，也有少部分物源来自华北克拉通北缘。根据该样品的谱值特征并结合古生物地层学及古地磁学成果，研究区林西组的沉积下限时代主要为中二叠世末，林西组的沉积时代主体应为晚二叠世，并可延至早三叠世初。结合区域地层对比和中亚造山带东段构造演化，认为古亚洲洋可能在晚二叠世最终闭合。

Detrital zircon U-Pb age of siltstone from Linxi Formation in Balinyouqi,Inner Mongolia : constraints on the final closure of the Paleo-Asian Ocean

In this paper, detrital zircon U-Pb ages were studied with the aims to reveal the formation ages and associated tectonic settings of clastic rocks from Linxi Formation in the north Xilamulun River, Balinyouqi, Inner Mongolia.The LA-ICP-MS results show that the 98 zircons grains show concordant ages of 252~315 Ma, 376~523 Ma, 752~1097 Ma, 1465~1694 Ma and 1833~2563 Ma.The youngest zircons age is 252 Ma, which indicates that the lower sedimentary age of the Linxi Formation is the Late Permian.The zircon age spectrum map, which includes the age information of both the southern margin of the Central Asian Orogenic Belt (CAOB) and northern margin of the North China Craton (NCC), showt that the stratum was characterized by multi-sources.This indicates that the materials in the Linxi Formation was mainly sourced from the south margin of the CAOB with minor from the northern margin of the NCC.The sample age information and the previous Paleontological stratigraphy and Paleomagnetic studies indicate that the sedimentary time of the Linxi Formation is the late Middle Permian to early Early Triassic, with the main sedimentary time of Late Permian.Combined with the comparison of regional strata and tectonic evolution in the eastern CAOB, the authors conclude that the Paleo Asian Ocean was likely final closed during the Late Permian.