Petrogenesis and tectonic implications of late Permian and Triassic granitoids on Hainan Island, South China

Hainan Island is a key part of the eastern Tethyan region and contains detailed geological information that can enhance our understanding of the tectonic evolution of this region since the late Palaeozoic. In this paper, we report geochronological, geochemical, and Sr-Nd isotopic data for granitoids from Baomei and Chahe in the northern part of Hainan Island. Three new zircon U-Pb ages of 243.3 +/- 1.7 Ma, 237.1 +/- 5.1 Ma, and 257.0 +/- 4.0 Ma were obtained for these granitoids. The late Permian Chahe granite (257 Ma) is weakly peraluminous to peraluminous, and has rare earth element patterns and Ga/Al and FeOT/MgO ratios typical of A-type granites formed in an extensional tectonic setting. The Middle Triassic Baomei granitoids (243-237 Ma) are weakly peraluminous, and exhibit a negative correlation between P2O5 and SiO2, which is typical of I-type granites. All the granitoids have EM II-type-enriched mantle Sr-Nd isotopic compositions, which indicate that they were derived from a mantle source that had experienced enrichment and metasomatism. Hainan Island was in an extensional tectonic setting from the late Permian to Middle Triassic when widespread A- and I-type granites were generated. We speculate that Hainan Island was mainly affected by the Tethyan tectonic domain during the Permian-Triassic, which involved closure of the Palaeo-Tethys Ocean, collision of the Indochina and South China blocks, and subsequent post-collisional extension.