Seafloor hydrothermal system and its magmatic setting in the western Pacific back-arc basins

The study of seafloor hydrothermal system and its magmatic setting can provide effective research support for understanding the material and heat exchange processes across the multi-spheric fluid-solid interfaces in the western Pacific. In order to reveal the magmatic activities, mineral deposition and environmental responses to plate subduction, the magmatic setting of Okinawa Trough hydrothermal systems, hydrothermal plume of Manus basin, isotopic composition of sulfide and basalt in back arc basins and mid-ocean ridges are carefully studied in this paper. The petrographic, mineralogical, major and trace elements, and isotopic composition for basalt, andesite, trachyandesite, dacite, rhyolite and their basic magmatic enclaves near the Okinawa Trough hydrothermal field have been carried out, whereas the hydrothermal plume and seawater measurement in PACMANUS and Desmos hydrothermal fields of the Manus basin studied. The results have successfully revealed the magmatic mixing process and time scale, the deep magmatic chamber and magma evolution process, the contribution of magma to the hydrothermal system in the Okinawa Trough as well as the influence of subduction serpentine on magmatic activity in the southern Ryukyu subduction zone. Melt inclusions are used as the mean to study the evolution of the back-arc basin magma, and the new evidence of the source of basaltic magma in the Okinawa Trough. The origin of iron, copper and zinc in the sulfide and basalts of the mid-ocean ridges and the back-arc basins, and the iron, copper, and zinc isotopic fractionation during sulfide formation and magmatic activity are discussed. The physical and chemical spatial pattern and material composition characteristics of the hydrothermal plume have been defined. It seems that the diffusion depth of the hydrothermal plume is affected by local seawater depth and bottom current, and the concentration anomaly of the dissolved Fe may remain for longer time than dissolved Mn during lateral plume dispersal. In the future, non-traditional stable isotopes and volatile analytical technology should be adopted for further understanding of the relationship between hydrothermal activity and magmatism under plate subduction environment taking the western Pacific as a research case so as to know more about the seafloor hydrothermal system and its ore-forming processes.