西太平洋弧后盆地的热液系统及其岩浆环境研究

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

研究海底热液系统及其岩浆环境,可为了解西太平洋流固界面跨圈层物质与热交换过程,揭示板块俯冲过程的岩浆活动和资源环境效应提供研究支撑。为此,研究了冲绳海槽热液活动的岩浆环境、马努斯海盆的热液柱以及弧后盆地和洋中脊背景下的硫化物与玄武岩的同位素组成,对冲绳海槽热液区附近玄武岩、安山岩、粗安岩、英安岩、流纹岩及其基性岩浆包体进行了岩相学、矿物学以及主量元素、微量元素和同位素组成分析,对马努斯海盆PACMANUS和Desmos热液区的热液柱及海水进行了测量,在海底热液区岩浆混合过程及时间尺度、透视冲绳海槽深部岩浆房及岩浆演化过程和岩浆对热液系统物质贡献研究方面获新进展,揭示了俯冲蛇纹岩对琉球构造带南部岩浆活动的影响,论证了熔体包裹体对弧后盆地岩浆演化的指示,获得了冲绳海槽玄武质岩浆来源新证据,揭示了弧后盆地与洋中脊硫化物和玄武岩中铁、铜、锌的来源及其同位素在硫化物形成和岩浆活动过程中的分馏情况,明确了热液柱的物理、化学空间结构与物质组成特征,以及热液柱的扩散受深度和底流流速的影响,且热液柱扩散过程中溶解铁浓度异常比溶解锰的维持时间更长。未来,发展非传统稳定同位素和挥发份测试技术,进一步了解西太平洋板块俯冲环境下热液活动与岩浆作用的关系,将有助于海底热液系统及其成矿过程研究获得新进展。

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 oreforming processes.