Triassic amphibolite-facies metamorphism in northeastern Hainan Island, South China

•Triassic medium-grade metamorphism is recognized in Hainan Island, the eastern Paleo-Tethyan tectonic domain.•Amphibolite-facies metamorphism of the Mulantou Metamorphic Complex took place at ca. 250–235 Ma.•Peak metamorphic conditions reached 717–771 °C and 4.4–5.8 kbar, equivalent to a geothermal gradient of approximately 30 °C/km.•Mulantou Triassic amphibolite facies metamorphism resulted from collision between the South China and Indochina blocks after closure of the Paleo-Tethys.