Implications for provenance and tectonic setting of the Middle–Late Mesozoic clastic sedimentary rocks in the Nanling Region, South China

Abstract

The South China Block (SCB) hosts numerous economically significant granite-related uranium deposits and critical metal mineralization, notably in the Nanling Region. This study investigates the petrogenesis, provenance, tectonic setting, and potential link to uranium mineralization of Middle–Late Mesozoic clastic sedimentary rocks from the Fengzhou Basin and surrounding areas, SCB. Field and petrographic observations reveal litharenite, arkose, and wacke, mostly cryptocrystalline and variably colored, alongside granoblastic-textured quartz sandstones, purple-red mudstones, and conglomerates dominated by granitic lithic fragments. Whole-rock geochemistry and detrital zircon U–Pb ages were used to interpret source weathering, provenance and source rock composition, and tectonic setting. Major and trace element ratios (e.g., ACNK, CIA, CIW, ICV, Th/U vs. Th) indicate moderate to intense weathering in sandstone and mudstone sources, but weaker weathering for conglomerates. Geochemical proxies (e.g., Al₂O₃ vs. TiO₂, La-Th-Sc, V-Ni-Th∗10, La/Yb vs. REE, La/Th vs. Hf, Th/Sc vs. Zr/Sr, REE patterns) suggest a dominantly felsic source, consistent with the Upper Continental Crust, with minor intermediate input. Detrital zircons yield concordant ages from ca. 2696 to 177 Ma, clustering into four age groups of 2696–2202 Ma, 1989–1087 Ma, 938–433 Ma, and 252–177 Ma, aligning with regional magmatic episodes and sedimentary units in the Nanling and Jiangnan orogens, Wuyi, and Yunkai domains. Tectonic discrimination diagrams using geochemical proxies (e.g., K₂O/Na₂O vs. SiO₂, DF1 vs. DF2, La-Th-Sc, Th-Sc-Zr/10 and Th-Co-Zr/10), along with the detrital zircon dating, suggest deposition occurred in a transitional setting, likely a back-arc or post-orogenic basin, marking a shift from compressional to extensional regimes between the Middle Jurassic to Late Cretaceous. Elevated REE, U, Th, and high U/Th, Rb/Sr, and Rb/Ba ratios, along with granite-derived lithic fragments, suggest provenance from uranium-enriched felsic sources, highlighting a genetic link between clastic sedimentation and regional granitoid-related uranium mineralization.