关键词: 碎屑锆石U-Pb年龄, 砂岩, 林西组, 大兴安岭中段, 沉积环境

Abstract: The Late Permian Linxi Formation is widely distributed in the northwest of Jalaid Banner, Middle Part of the Greater Khingan Mountains. The formation is mainly composed of arkose，siltstone，feldspar lithic sandstone containing pebbled sandstone, and limestone of different scales, and the middle part contains abundant bivalves and plant fossils. In this study, LA-ICP-MS U-Pb dating was carried out for the arkose litharenite sandstone in the lower part of the Linxi Formation, and a total of 98 effective ages were obtained. Based on the test data, they are roughly divided into the following groups according to the characteristics of age value and frequency distribution: Upper Devonian-Late Permian（380.0-246.1 Ma）,Silurian-Late Cambrian（489.0-413.8 Ma）,  Mesoproterozoic-Neoproterozoic（1 239.5-808.1 Ma）, Paleoproterozoic（2 554.0-1 784.3 Ma）. The above six groups of age peaks are basically consistent with the time of the regional magmatic activities. The comprehensive study shows that the lower deposition limit of the Linxi Formation in the study area is in（253.4±1.5） Ma, the remaining zircons are mainly from the Xingmeng-Mongolia orogenic belt, the Northern Margin of the North China plate, and the various blocks in Northeast China. The detrital zircons with 1.8 and 2.5 Ga ages are more likely to have come from the northern margin of the North China plate. The collision of the North China plate and the Siberian plate was completed before（253.4±1.5）Ma, the ancient Asian Ocean was closed, and the Xingmeng Trough was formed. The discovery of the marine  oncolytic in the Linxi Formation also confirms that the marine environment should still be dominant in the Middle Part of the Greater Khingan Mountains in the Late Permian, then it gradually changed into the continental sedimentary environment.

Key words: detrital zircon U-Pb chronology, sandstone, Linxi Formation, the Middle Part of the Greater Khingan Mountains, sedimentary environment