桂东北地区鹰扬关群的构造属性:来自下龙组条带状磁铁石英岩的年代学约束OA

The Yingyangguan group in northeastern Guangxi,serving as a crucial area for reconstructing the early tectonic evolution of the South China Block,has long been subject to academic debate regarding its chrono-logical classification and tectonic affinity.To address this,we conducted detrital zircon U-Pb dating and Hf iso-tope analysis on banded iron formation(BIFs)from the Xialong Formation of the Yingyangguan Group,which exhibit continuous and traceable stratigraphic sequences.Three BIFs samples(YY21063,YY21074,and YY2302)yielded similar detrital zircon U-Pb age spectra,with dominant age peaks at 0.72-0.90 Ga,and subordi-nate populations at 0.90-1.30 Ga,1.62-1.99 Ga,2.12-2.36 Ga,and 2.43-2.64 Ga.Two samples(YY21063 and YY2302)displayed comparable zircon Hf isotopic compositions,with εHf(t)values ranging from-21.92 to 11.68,and-12.80 to 10.73,respectively.Their two-stage Hf model ages(TDM2)varied between 0.92-3.85 Ga and 1.09-3.31 Ga,indicating that the detrital materials were predominantly derived from the reworking of Mes-Paleo-proterozoic and Archean crustal sources.The youngest detrital zircon ages from all three samples consistently constrained the maximum depositional age of the Xialong Formation at 720 Ma,thereby confirming the Neopro-terozoic age of the Yingyangguan Group.The dominant 0.72-0.90 Ga zircon age population suggests that the pri-mary provenance was likely associated with Neoproterozoic magmatic events along the southeastern margin of the Yangtze Block.The continuous and traceable banded iron formations in the Xialong Formation indicate that the Yingyangguan Group represents a coherent sedimentary sequence rather than a tectonic mélange.Combined with the provenance signatures,we propose that the Yingyangguan Group formed in a rift-related tectonic setting,fur-ther elucidating the Neoproterozoic tectonic evolution of the South China Block.