Cryogenian provenance and tectonic setting evolution of South Qinling Belt: Insights from detrital zircon UPb geochronology and LuHf isotope analysis

Abstract

Significant uncertainties persist regarding the depositional environment, tectonic affinity, and geodynamic significance of the extensively exposed Neoproterozoic Yaolinghe Group rocks in the South Qinling Belt (SQB) and the northern margin of Yangtze Block (NYZB), hindering the interpretation of their sedimentary record, regional tectonic evolution, and role in Rodinia assembly-breakup dynamics. This study conducted comprehensive investigations on sedimentary rocks in both the Zhenping and Langao areas. By utilizing LA-ICP-MS zircon UPb isotope analysis and integrating previous data, our findings indicate that these sedimentary rocks were deposited during the early to middle Cryogenian period. LuHf isotope analysis reveals a wide range of ε_Hf(t) values for sample ZP-4, ranging from −17.22 to 10.47 with an average of −4.7, indicating reworked ancient crust as their source material. Sample LG-6 from Langao exhibits a range of ε_Hf(t) values, ranging from −18.56 to 11.18, with an average value of −2.7; a subset of younger detrital zircons (<750 Ma) displays positive ε_Hf(t) values, suggesting the incorporation of material eroded from juvenile crust. Furthermore, the presence of sedimentary rock fragments within the Yaolinghe Group deposits suggests the exhumation and subsequent redeposition of ancient sedimentary sequences, such as the Wudang Group, Nantuo Formation, and Liantuo and Gucheng Formations, took place along the northern margin of the Yangtze Block and South Qinling Belt. Notably, the Zhenping area lies within an intracontinental rift zone. In contrast, the Langao area in the SQB appears to have been closer to the outer continental margin and significantly influenced by adjacent sources, including early or contemporaneous magmatic zones. In conjunction with regional data, we propose that the SQB transitioned from early subduction accretion to late-stage extensional rifting during the Cryogenian. This sequence of events may represent the response of the marginal blocks of the Rodinia supercontinent to the final rifting during the Middle to Late Neoproterozoic.