Early transgressive-basin provenance reorganization and tectonic implications: detrital zircon U-Pb evidence from the Lower-Middle Devonian of Qujing, South China Block

Lower‑Middle Devonian sandstones in Qujing, eastern Yunnan, archive provenance evolution during Devonian transgression across the southwestern South China Block. We performed detrital zircon LA‑ICP‑MS U‑Pb dating, trace‑element analysis and framework‑grain modal counting on six samples from the Xiaxishancun, Guijiatun, Xujiachong and Haikou Formations, obtaining 531 concordant ages from 634 analyses. Age spectra are dominated by Neoproterozoic zircons peaking at 805–820 Ma, accompanied by subordinate early Paleozoic peaks (515–535 Ma, local 448 Ma) and minor older Precambrian populations. The lower succession yields complex age signals indicative of mixed basement detritus from the western Yangtze‑Kangdian and western Jiangnan domains, while the upper succession is overwhelmingly dominated by 805–820 Ma grains, recording a shift toward focused sourcing from western Jiangnan Neoproterozoic rocks. Zircon geochemistry supports magmatic continental crust sources. Q‑F‑L data demonstrate quartz‑rich, recycled‑orogen affinities, implying significant sediment recycling from uplifted orogenic and basin‑margin strata. Coupled with Paleo‑Tethyan tectonic evolution, the Qujing succession records an Early Devonian shift from compartmentalized basins with heterogeneous, mixed local provenance to an interconnected transgressive basin with a unified Neoproterozoic sediment source.