Permian age of the Wudaogou Group in eastern Yanbian: detrital zircon U-Pb constraints on the closure of the Palaeo-Asian Ocean in Northeast China

摘要

The Wudaogou Group in eastern Yanbian, Northeast China, plays a key role in constraining the timing and eastward termination of the Solonker-Xra Moron River-Changchun Suture, where the Palaeo-Asian Ocean closed. The Wudaogou Group consists of schist, gneiss, amphibolite, metasedimentary, and metavolcanic rocks, all of which underwent greenschist-to epidote-amphibolite-facies regional metamorphism, with some hornfels resulting from contact metamorphism. To determine the age of deposition, the timing and grade of metamorphism, and the tectonic setting of the Wudaogou Group, we investigated the petrography and geochronology of the metamorphic rocks in this group. Zircons from the metasedimentary rocks of this group can be divided into metamorphic zircons and detrital zircons of magmatic origin. U-Pb ages of metamorphic zircons dated by LA-ICP-MS vary from 249 ± 4 to 266 ± 4 Ma, approximating the age of regional metamorphism in the eastern Yanbian area. Detrital zircons yield U-Pb ages ranging from 253 ±5 to 18±5 Ma, and indicate that the provenance of the Wudaogou Group experienced four tectonic-thermal events between 818 and 253 Ma: Neoproterozoic (ca. 818-580 Ma), Cambro-Ordovician (ca. 500-489 Ma), Devonian-Carboniferous (ca. 422-300 Ma), and middle-late Permian (ca. 269-253 Ma). The youngest detrital zircon, with a U-Pb age of 253 ± 5 Ma, defines the maximum depositional age of the Wudaogou Group. The presence of the Cambro-Ordovician and Neoproterozoic detrital zircons implies that the source of the Wudaogou Group had an affinity with Northeast China, which leads us to conclude that the Solonker-Xra Moron River-Changchun Suture extends from Wangqing to Hunchun in eastern Yanbian, and that the Palaeo-Asian Ocean may have closed at the end of the Permian or Early Triassic period.