冀北闪长质岩石的锆石SHRIMP U-Pb年龄：晚古生代岩浆弧的地质记录

Zircon SHRIMP U-Pb age of the dioritic rocks from northern Hebei:the geological records of late Paleozoic magmatic arc.

华北克拉通北缘的丰宁-承德地区分布着许多被认为是古元古代的片麻状闪长质-石英闪长质-花岗闪长质侵入体,新的年代学资料揭示这些侵入体中许多是晚古生代的产物。本次工作从京北喇叭沟门闪长岩体和丰宁天桥含石英闪长岩体中分别获得了(288.0±4.8)Ma和(279.5±5.6)Ma的锆石SHRIMP U-Pb年龄。这些钙碱性岩石的存在表明华北克拉通北缘在早二叠世是一条安第斯型的活动大陆边缘。综合分析冀北地区晚古生代侵入岩的侵位时代和变形特点,结合该地区晚古生代发生变形变质作用的年龄信息,推测华北克拉通北侧的古亚洲洋在晚二叠世末封闭,随后进入了主造山期之后的构造松弛阶段。

A lot of gneissic diorite, quartz-diorite and granodiorite occurred on the northern part of Hebei Province （northern Hebei）, the northern margin of North China Craton, which was once regarded as intruding at early Proterozoic. Recently, chronological data reveal that many of the dioritic plutons intruded in late Paleozoic. The zircon SHRIMP U-Pb age of Labagoumen diorite from the northern part of Huairou county, Beijing, is （288.0±4.8） Ma （95% conf. , MSWD = 1.12）, and the one of Tianqiao quartz-bearing diorite from Fengning county, Heibei province, is （279.5±5.6） Ma （95% conf. , MSWD = 0.57 ）. These calc-alkali intrusive rocks occurred on the northern margin of North China craton indicate a tectonic setting of Andean active continental margin. Based on the emplaced ages and structural characteristic of late Paleozoic intrusive rocks in conjunction with the age information of deformation and metamorphism occurred on northern Hebei, we conclude that Paleo-Asian ocean to the north of North China Craton closed at the terminal of Lopingian Epoch （ late Permian）, subsequently, the evolution of Central Asian Orogenic Belt turned into the relaxed tectonic stage following the peak of orogenesis.