Permian-Triassic felsic magmatism in the Qiongdongnan Basin: Implications for the tectonic properties and evolution of the northern continental margin of the South China Sea

The large-scale Permian-Triassic magmatic rocks in the Qiongdongnan Basin provide a probe for studying the paleotectonic properties and evolution processes of the northern continental margin of the South China Sea. This study focuses on the felsic magmatic rocks, and conducts research on the petrology, zircon U-Pb geochronology, whole-rock geochemistry, and zircon Lu-Hf isotope, aiming to explore the spatiotemporal framework, petrogenesis, and dynamic background of the Permian-Triassic magmatic rocks in the Qiongdongnan Basin. LA-ICP-MS zircon U-Pb geochronology indicates three episodic felsic magmatism occurred in the Qiongdongnan Basin (271 217Ma), i. e., Permian-Early Triassic, Middle Triassic, and Late Triassic, exhibiting a migration trend from south to north. The Permian-Early Triassic felsic rocks have low FeO/MgO and 10000 x Ga/Al ratios with strongly depleted elements such as Zr, Hf, Nb, Ta, etc., belonging to the typical I-type granites in continental margin arc. The Middle Triassic and Late Triassic felsic rocks have high SiO2, Mg-#, 10000 x Ga/Al, and FeO/MgO ratios, mostly belonging to A-type granites. Besides, the Permian-Early Triassic felsic rocks have low Hf isotopes (epsilon(Hf)(t) = 7. 61 similar to 0. 65), while the Middle to Late Triassic felsic rocks have high Hf isotopes. Petrogenesis study reveals that the studied Permian-Early Triassic I-type granites were derived the partial melting of ancient crustal rocks, while the Middle Triassic and Late Triassic A-type granites either originated from the melting of the ancient felsic continental crust, or sourced from the juvenile crust or crust-mantle interaction. Comprehensive study shows that the northern continental margin of the South China Sea was mainly controlled by the Paleo-Tethys orogeny during the Permian-Triassic Period, and underwent dynamic processes such as the Paleo-Tethys oceanic subduction in the Permian-Early Triassic, the collision between the Indosinian and South China plates in the Middle Triassic, and post-collisional extension in the Late Triassic.