Provenance and Tectonic Setting of the Mesoproterozoic Pudeng Formation in the Western Yangtze Block

The Yangtze Block provides a natural window into the tectonic evolution of Precambrian continental crusts. The Julin Group is a dominant Precambrian stratigraphic unit in the southwestern block, the depositional age of which is still poorly constrained. The lowest sequence of this group, the Pudeng Formation, is primarily composed of mica-quartz schists and quartzites intruded by a biotite monzogranite. LA–ICP–MS zircon U–Pb ages of biotite monzogranite and detrital zircons constrain the deposition of the Julin Group to between 1099 and 1052 Ma. Geochemical compositions of the mica-quartz schists and quartzites display high δCe, ΣREE, Th/Sc, and Th/U, along with low δEu, La/Sc, Ce/Th, and Al₂O₃/(Al₂O₃ + Fe₂O₃) ratios, indicating their derivation from felsic volcanic protoliths in a passive continental margin setting. The detrital zircons show distinct age peaks at 2.5, 1.85, and 1.6 Ga, with their source regions primarily located along the western and northern Yangtze Block. Integrating the magmatic records within the Yangtze Block with the ages and ε_Hf(t) values of detrital zircons indicates that the tectonic setting of the western Yangtze Block evolved from a subduction-related arc at ~2.5 Ga to an orogenic belt at ~1.86 Ga and subsequently to intracontinental extensional (rift) environments at ~1.6 Ga and ~1.2 Ga. This evolution reflects the geodynamic transition from the Arrowsmith orogeny to the assembly and development of the Columbia and Rodinia supercontinents.