吉林省下三叠统卢家屯组LA-ICP-MS锆石U-Pb定年及其地质意义

卢家屯组按岩性组合自下而上分为影背山砾岩段、漏斗山杂色岩段、杨树河子黑色岩段,前人采集到的Palaeanodonta-Palaeomutela动物群、Pleuroneia? sp.和叶肢介等生物化石组合指示时代为二叠纪。本次对九台市影背山双顶山卢家屯组建组剖面下、中、上段进行了系统的碎屑锆石U-Pb同位素年代学研究,证实卢家屯组由下至上存在3个最小锆石年龄峰值,分别为(283.4±7.9)、(262.4±3.9)、(255.5±5.8) Ma,确定了卢家屯组的上限为晚二叠世。根据卢家屯组中碎屑锆石存在1 800 Ma和2 500 Ma左右的典型华北板块基底年龄,认为华北板块北缘与其北侧地块群最终闭合时间应为P₃-T₁。

Zircons LA ICP MS U Pb Ages of the Lower Triassic Lujiatun Group and Its Geological Significance in Jilin Province

According to the associated lithologic feature, the Lujiatun Formation is divided into Yingbeishan conglomerate section, Loudoushan variegated rock section, and Yangshuhezi black rock section. Based on the fossil assemblages, such as Palaeanodonta-Palaeomutela fauna, Pleuroneia? sp. and the conchostracan, it was formed in Permian. A systematic U-Pb isotopic chronology of the detrital zircon is studied for the Bottom, Middle, and Upper Section of the construction profiles of Lujiatun Formation in Yingbeishan-Shuangdingshan in Jiutai. The results show three minimum zircon age peaks at (283.4±7.9) Ma, (262.4±3.9) Ma, and (255.5±5.8) Ma from the bottom to the top. It can be confirmed that the top section of the formation belonged to the Late Permian. The detrital zircon ages of 1 800 Ma and 2 500 Ma in the Lujiantun Group are typical for the base plate age of North China Plate. In conclusion, the plate closure happened probably during P₃-T₁ between the northern margin of North China Plate and the group of plates to its north.