There are very few studies on the granites formed in Late Permian in Hainan (海南)Island. Petrology, geochronology and geochemistry research on Late Permian granites in Chahe (叉河) area, Hainan Island will be reported in this article. The results show that, Chahe granites formed in 251 Ma, are riched in SiO2, alkali, Fe2O3 while depleted in MgO and CaO, with low Sr and high Yb, and have all the features consistent with A-type granite. The forming of Chahe granites may suggest that Hainan Island was already in post-orogenic setting in Late Permian.
This work studies new petrological and geochemical data and zircon U-Pb ages for bimodal intrusive rocks from Xinglong region, Hainan Island. Zircon U-Pb dating yields mean 238 U/ 206 Pb ages of 238 ± 2 Ma and 234 ± 2 Ma for diabasic and granitic phases, respectively, representing the Middle Triassic emplacement. The diabase and granite bodies were formed from discrete mafic and acidic magma sources that experienced local mechanical mixing at their mutual contacts. Although SiO 2 content of intrusions is bimodal, trace element ratios indicate that both were formed in a post-orogenic extensional setting. Sr-Nd isotopic composition reflects a shared EMII type enriched mantle source component, possibly influenced by subduction-fluid metasomatism.
