关键词: 华北板块北缘, 晚古生代, 碎屑锆石, U-Pb-Hf同位素, 地壳厚度, 万宝岩组, 古亚洲洋

Abstract: In this paper, the metamorphic siltstones of the Wanbao Formation in Dunhua, Jilin Province, were studied. The research included detailed analysis of detrital zircon trace elements and U-Pb-Hf isotopes to determine the sedimentary timeframe and source characteristics of the Wanbaoyan Formation. Further, the variation pattern of Late Paleozoic crustal thickness, inferred from detrital zircon trace elements, was used to explore the Late Paleozoic tectonic evolution history of the eastern part of the Northern margin of the North China plate. The Wanbao Formation consists of interbedded marble, metamorphic siltstone and metamorphic fine sandstone. The detrital zircon dating results show that the youngest peak age of the Wanbao Formation is ~316 Ma, in addition to peak ages of 355 Ma, 398 Ma, 1 842 Ma and 2 360 Ma. The Paleozoic detrital zircons (409-312 Ma) have negative  εHf(t) values (-15.32--1.60) and a TDM2 age (2 293-1 480 Ma) in the Neo-Paleozoic-Paleozoic period, with the age of the amphibolite bodies intruding Wanbao Formation is 276 Ma. The comprehensive study concludes that the depositional timeframe of Wanbao Formation in Dunhua area is 312-276 Ma, i.e., the Early Permian period, and shares similarities in depositional timeframe and rock assemblage characteristics with the Miaoling Formation in Yanbian area. The Paleozoic detrital zircons in Wanbao Formation are derived from partial melting of materials from the Paleozoic-Tertiary crystalline basement of the North China plate. Furthermore, the prevalence of Precambrian detrital zircons (62.9%) implies the presence of Precambrian crystalline basement of the North China plate in or near the Dunhua area. The crustal thickness calculation shows a similar trend in Late Paleozoic crustal thickness between Dunhua and Inner Mongolia regions, indicating synchronized evolutionary histories. The crust reached its maximum (80 km) thickness at ~245 Ma, suggesting the final closure of the Paleo-Asian Ocean.

Key words: Northern margin of the North China plate;Late Paleozoic;detrital zircons;U-Pb-Hf isotopes;crustal thickness, Wanbaoyan Formation;Paleo-Asian Ocean