Age And Provenance Of The Early Paleozoic Sedimentary Formation In The Northern Jiamusi Massif:Evidence From U-Pb Ages And Hf Isotope Compositions Of Detrital And Magmatic Zircons

In this paper,we present the LA-ICP-MS/SIMS U–Pb ages and Hf isotope compositions of zircons from metasedimentary rocks and intrusive rocks within the Jinyinku Formation in the northern Jiamusi Massif,and our aim was to constrain the depositional ages and provenance of the strata.All the zircons separated from three samples are euhedral–subhedral in shape and display striped absorption and/or oscillatory growth zoning patterns in CL images,implying their magmatic origin.The dating results indicate that the 72 analytical spots of zircons from a sericite schist yielded ages ranging from 1955 Ma to 457 Ma,which can be subdivided into five age populations at 814,757,568,491 and 463 Ma.Their?_Hf?t?values and one-stage model ages(T_DM1)as well as two-stage model ages(T_DM2)range from–13.9 to–0.1,827 to1307 Ma and 2411 to 1715 Ma,respectively.Zircons from aplite and diabase that intrudes the Jinyinku Formation yield weighted mean ages of 263 Ma and 267 Ma,respectively.Additionally,the former has?_Hf?t?values of+0.9⁺2.0 and T_DM2 ages of1110¹047 Ma,whereas the latter has?_Hf?t?values of–7.7⁺6.4 and T_DM1 ages of1206⁶62 Ma.Combined with the occurrence of the granitoids with the ages of⁴30Ma within the Jiamusi Massif,zircon age populations,and Hf isotopic compositions,we conclude that the Jinyinku Formation formed between 463 Ma and 430 Ma?i.e.,Late Ordovician to Early Silurian?and was sourced mainly from Neoproterozoic and Early Paleozoic terrane in the Jiamusi Massif and adjacent regions.Taking account characteristic of sedimentary formation and regional tectonic evolution,we conclude that the Jinyinku Formation formed in a passive continental margin setting.