关键词: 孙吴—嘉荫盆地, 乌云组, 孙吴组, U-Pb年代学, 地球化学, 物源, 构造背景

Abstract: In order to reveal the provenance and geological significance of the Paleogene in Sunwu-Jiayin basin, this paper studies the detrital zircon dating and geochemical characteristics of samples from Paleogene Wuyun and Sunwu Formations. The age peaks of 72 measuring points of detrital zircons in Wuyun Formation are 57, 97, 188, 262, 380, 496, and 1 854 Ma, and the age peaks of 64 measuring points of detrital zircons in Sunwu Formation are 52, 65, 92, 181, 220, 472, 1 884, and 2 318 Ma, indicating that the provenance of Wuyun Formation and Sunwu Formation is complex and diverse. The contents of MgO, Al2O3, CaO, K2O and Fe2O3 in the samples are relatively low. The chemical alteration index CIA value ranges from 64.30 to 81.72, and the composition variation index ICV value ranges from 0.44 to 0.70. Th/Sc values are positively correlated with Zr/SC values. The total amount of rare earth elements (∑REE) changes from 97.44×10-6 to 154.87×10-6 and 85.65×10-6 to 315.62×10-6, respectively. La/Yb ratios vary from 10.94 to12.84 and 13.26 to 20.74. Combined with the characteristics of major, trace and rare earth elements and the age peaks of detrital zircon, it is concluded that the Paleogene sources are the Paleoproterozoic geological body in the eastern margin of Songnen-Zhangguangcai range Massif and the felsic igneous rocks produced by magmatic events in various times. The tectonic background of the source area is active continental margin and continental island arc. There are apparent differences between Paleogene and Upper Cretaceous provenance in the basin. Combined with the characteristics of regional tectonic evolution, we speculated that it was caused by the Pacific plate retreat or drawback and subducted direction changes in the process of Pacific plate subducting to the East Asian continent. 

Key words: Sunwu-Jiayin basin, Wuyun Formation, Sunwu Formation, U-Pb chronology, geochemistry, provenance, tectonic setting