Zircon U–Pb Ages and Geochemistry of Diaoluoshan Granite, Hainan Island: Implications for Late Cretaceous Tectonics in South China

Hainan Island has experienced a superposition of multiple phases of tectonic movements and magmatic activities, leading to numerous controversies regarding the genesis, spatiotemporal distribution, and tectonic setting of its Yanshanian granites. Accurately determining the characteristics of magmatic rocks during this period is crucial for clarifying the regional tectonic evolution. This study focuses on Diaoluoshan granite in the southeastern part of Hainan Island. Through petrological, mineralogical, zircon U-Pb geochronological, and geochemical analyses, it aims to identify the genetic type, formation age, and magma source properties of this pluton, thereby revealing the Late Yanshanian tectonic setting of Hainan Island. The results show that the zircon U-Pb dating of Diaoluoshan granite yields an age of 102.5 ± 2.8Ma, indicating its formation in the late Early Cretaceous. This granite is a high-K calc-alkaline I-type granite, with silica (SiO2) content ranging from 63.9% to 77.3%. The pluton exhibits significant negative anomalies of Ta, Nb, P, and Ti, as well as relatively obvious positive anomalies of Rb, Th, U, and K. The biotite in the granite has a magnesium oxide (MgO) content ranging from 12.84% to 13.13%, showing characteristics of crust–mantle material mixing. The magma of this pluton was derived from the partial melting of the lower continental crust mixed with the uprising and underplating mantle mafic magmas, driven by the subduction of the Paleo-Pacific Plate and its slab rollback. This study confirms that during the Late Yanshanian, Hainan Island was in an extensional rift environment driven by the subduction of the Paleo-Pacific Plate and its slab rollback, but without a well-developed volcanic front. It provides key geological evidence for the study of Yanshanian tectono-magmatic evolution in South China.