内蒙古扎鲁特旗上二叠统林西组碎屑锆石LA-ICP-MS U-Pb测年及意义

研究区位于西拉木伦河-长春-延吉断裂以北，区内发育有巨厚的上二叠统林西组，岩性为灰、灰黑、黄绿色的砂板岩组合.研究其年代学特征对确定该区大地构造背景具有重要的指示意义.对采自林西组的砂岩样品进行了锆石LA-ICP-MS U-Pb测年.结果显示，其年龄分布在5个年龄区间：252~300 Ma、305~423 Ma、431~555 Ma、600~999 Ma、1037~2460 Ma.最年轻的年龄为252 Ma，指示林西组沉积时间下限为252 Ma.上述碎屑锆石的年代学研究表明，扎鲁特旗地区晚二叠世林西组物源既有东北地区的变质基底以及其后的构造岩浆事件信息，也包含有南侧华北板块北缘信息，说明在晚二叠世晚期沿西拉木伦河缝合带华北板块北缘与其北侧地块群完成最终碰撞拼贴.

ZIRCON LA-ICP-MS U-Pb DATING AND ITS IMPLICATION OF UPPER PERMIAN LINXI FORMATION IN JARUD QI,INNER MONGOLIA

The study area is located in the north of Xar Moron River-Changchun-Yanji fault where the huge thick Upper Permian Linxi Formation is developed, with the lithologic assemblage of gray, grayish black and yellow-green sandy slate. The research on its chronological characteristics is of important significance for determination of the geotectonic setting. The authors analyze the sandstone samples from Linxi Formation with zircon LA-ICP-MS U-Pb dating. The results show that the ages are distributed in 5 age ranges: 252-300 Ma, 305-423 Ma, 431-555 Ma, 600-999 Ma and 1037-2460 Ma. The youngest age of 252 Ma indicates the lower limit of sedimentary time for Linxi Formation. The study above shows that the provenance of Late Permian Linxi Formation in Jarud Qi area reflects the information of both the metamorphic basement and following tectonomagmatic event in Northeast China and the northern margin of the North China Plate, suggesting that the Linxi Formation completed the final collision and collage along the northern margin of the Xar Moron River suture zone between North China Plate and the blocks on north in the Late Permian.