ZIRCON SHRIMP U-Pb AGE OF THE DIORITIC ROCKS FROM NORTHERN HEBEI: THE GEOLOGICAL RECORDS OF LATE PALEOZOIC MAGMATIC ARC

Abstract

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.