Petrogenesis and geological significance of migmatitic gneiss in Mulantou area, Hainan Island

Abstract

In the coastal area of Pujian to Mulantou on Hainan Island, a set of medium to deep metamorphic rocks (Mulantou complex) has been discovered, composed of migmatite, dolomite, shale, and amphibolite, with migmatite being the predominant lithology. This study selected well-developed and typical migmatitic gneisses as the research focus and conducted systematic zircon U-Pb isotope dating and petrological and geochemical studies. The results indicate that the protolith of the Mulantou migmatitic gneisses was intermediate basic volcanic rock formed around 276 Ma. These rocks exhibit geochemical characteristics of island-arc calc-alkaline basalt, suggesting a tectonic setting related to the subduction of the Paleo-Tethys Ocean. Early anatectic metamorphism occurred around 261 Ma, indicating a tectonic environment related to the collision between the South China Block and the Indochina Block. Later metamorphism took place around 248 Ma, signifying a tectonic environment associated with extension following the collision between the South China Block and the Indochina Block. Therefore, the Mulantou migmatitic gneisses preserve a comprehensive record of the tectonic evolution in Hainan Island from the Early Permian to the Early Triassic. They represent the geological consequences of events such as the closure of the Paleo-Tethys Ocean, the collision between the South China Block and the Indochina Block, and the subsequent extension. The discovery of these rocks provides new insights into the eastern extension of the Song Ma suture zone.

Keywords

• hainan island
• migmatitic gneiss
• early permian-early triassic
• suture zone
• paleotethys