佳木斯地块北部早古生代沉积建造的时代与物源:来自岩浆和碎屑锆石U-Pb年龄及Hf同位素的制约

本文对出露于佳木斯地块北部金银库组变沉积岩和侵入其中的火成岩脉体中的锆石进行了系统的LA-ICP-MS/SIMS U-Pb定年和Hf同位素研究，旨在限定金银库组的沉积时限，并揭示其物源及沉积环境。3个样品中锆石呈自形-半自形，显示典型的岩浆生长环带或条痕状吸收，暗示其岩浆成因。研究结果显示:采自金银库组绢云母片岩中的碎屑锆石72个分析点给出1 955~457 Ma的年龄区间，主要峰期年龄为814、757、568、491和463 Ma，其ε_Hf（t）值为-13.9~-0.1，Hf同位素一阶段模式年龄T_DM1和二阶段模式年龄T_DM2分别为1 827~1 307 Ma和2 411~1 715 Ma。采自侵入金银库组的花岗细晶岩和辉绿岩分别给出了263和267 Ma的结晶年龄，前者的ε_Hf（t）值为0.9~2.0，Hf同位素二阶段模式年龄T_DM2为1 110~1 047 Ma；后者的ε_Hf（t）值为-7.7~6.4，Hf同位素一阶段模式年龄T_DM1为1 206~662 Ma。结合佳木斯地块及邻区约430 Ma火成岩的存在和金银库组中该期碎屑锆石的缺乏以及碎屑锆石年龄众数及其Hf同位素组成，我们认为金银库组的形成时代应为晚奥陶世至早志留世（463~430 Ma），形成于被动大陆边缘背景，沉积物源主要来自佳木斯地块及其邻区的古元古代和早古生代早期火成岩。

Age and Provenance of Early Paleozoic Sedimentary Formation in 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 detrital zircons from the metasedimentary rocks and intrusive rocks within the Jinyinku Formation in the northern Jiamusi massif to constrain the depositional ages and provenance of the strata.All the zircons separated from our 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 yield ages between 1 955 Ma and 457 Ma that can be subdivided into five age populations with peaks at 814,757,568,491,and 463 Ma.Their JHf (t) values and two-stage model ages (TDM2) range from-13.9 to-0.1 and from 2 411 to 1 715 Ma,respectively.The zircons from aplite and diabase that intruded in the Jinyinku Formation yield weighted mean ages of 263 Ma and 267 Ma,respectively.Additionally,the former has the JHf (t) values of 0.9-2.0 and TDM2 ages of 1 110-1 047 Ma;whereas the latter has the JHf (t) values of-7.7-6.4 and TDM1 ages of 1 206-662 Ma.In consideration with the occurrence of the granitoids with the ages of ～ 430 Ma 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) in a passive continental margin setting,and sourced mainly from Neoproterozoic and Early Paleozoic terrane in the Jiamusi massif and adjacent regions.