大兴安岭中段扎兰屯群浅变质岩的物源分析及构造意义OA

The Zhalantun island arc,situated in the central segment of Da Hinggan Mountains,hosts extensive exposures of Zhalantun Group low-grade metamorphic rocks and Early Palaeozoic arc-related magmatic suites,making it crucial for understanding the tectonic evolution of the Xing'an accretionary terrane.In this study,we conducted zircon U-Pb dating,whole-rock geochemistry,and Hf isotope analysis on muscovite quartz schist and fine-grained diorite from the Zhalantun-Arongqi area.Results indicate that protoliths of the muscovite quartz schist were sedimentary rocks(sandstone and greywacke)deposited during the late Early Paleozoic.The fine-grained diorite yielded a crystallization age of 521.8±2.4 Ma,confirming a genetic affinity with the Cambrian arc-volcanic belt of the Zhalantun island arc.Cambrian zircons from both the muscovite quartz schist and fine-grained diorite exhibit consistent Hf isotope signatures,characterized by variable positive and negative εHf(t)values indicative of a subduction-related magmatic source.Detrital zircon ages from the muscovite quartz schist can be categorized into four populations:① 475～427 Ma,derived from Early Paleozoic arc magmatic rocks within the Xing'an accretionary terrane;② 621～490 Ma(peak at～515 Ma),sourced from the Cambrian arc-volcanic belt;③ 996～756 Ma,primarily contributed by the Erguna block;and ④ 3313～1287 Ma,likely originating from both the Erguna and Songnen blocks.The low-grade metamorphic rocks of the Zhalantun Group exhibit unimodal detrital age distributions and proximal depositional characteristics consistent with a back-arc basin setting along an active continental margin,revealing the existence of an Early Paleozoic trench-arc-basin system in the Zhalantun island arc.