内蒙古东北部巨日河地区早—中三叠世碎屑锆石年龄及其地质意义

对内蒙古东部扎鲁特旗巨日河地区原定为上二叠统林西组砂岩样品的碎屑锆石LA--ICP--MS U--Pb年代学分析,发现所取两组样品均存在明显的三叠纪年龄峰值,分别为~244 Ma(ZL010)、~250Ma(ZL011),表明在该地区存在早、中三叠世沉积,原定为二叠纪的地层实为三叠系。两组样品的最小年龄分别为242±4 Ma(ZL010)、241±4 Ma(ZL011),限定了沉积的下限年龄为中三叠世。结合大兴安岭中部地区零星出现的早、中三叠世陆相化石的证据,进一步确认在内蒙古东北部大兴安岭地区存在早、中三叠统,其大面积缺失的原因,推测为该区域在三叠纪末发生了大规模构造抬升运动,导致三叠系遭受强烈剥蚀。

Detrital zircons from Early-Middle Triassic sandstones in Jurihe area of northeastern Inner Mongolia and its tectonic implications

In this paper， two groups of sandstone samples from the Jurihe area in Jarud Banner， Inner Mongo- lia，have been collected and examined by the zircon LA- -ICP- -MS U- -Pb dating which were originally regarded as the Upper Permina Linxi Formation． Both of the two groups of samples showed significant Triassic age peak，i. e. ～244 Ma for sample ZL010 and ～250 Ma for sample ZL011，which indicates that the studied area once existed Early- Middle Triassic sedimentation and the original scheduled Permian strata was Triassic actually． Moreover，the youngest ages of 242 ±4 Ma (sample ZL010) and 241 ± 4 Ma (sample ZL011) have been obtained，suggesting that the lower limit age of the deposit was Middle Triassic． Combining with the previously discovered Early and Middle Triassic continental fossil evidences in the middle part of the Great Khingan Mountains，we concluded that the Early-Middle Triassic sedimentation were probably widespread in the Great Khingan Mountains，northeastern Inner Mongolia． Subsequently， the large- scaled tectonic uplift movement took place in the Great Khingan Mountains in Late Triassic，leading to the intensity denudation of the Triassic strata in Jurihe area．