Reflections on Model of Modern Seafloor Hydrothermal System

Wang Shujie; Zhai Shikui; Yu Zenghui; Guo Kun; Zhang Xia

Abstract：Modern seafloor hydrothermal activity is generally accompanied by magmatism.Traditional hydrothermal system model hypothesizes that seawater penetrates through the rifts or cracks,then is heated and reacts with the surrounding rocks gradually leaching out metal elements from the rocks and resulting in the formation of metal-rich,acidic and reductive hydro-thermal fluid.Subsequently,the heated fluid moves up along a series of fissures and erupts directly out of the ocean floor lead-ing to precipitations of hydrothermal sulfides.This model reasonably accounts for the existence of fluid,channels and heat sources which are the three fundamental elements of modern seafloor hydrothermal system,and is in accord with many phe-nomena we have observed so far.However,differences in rock permeability,hydrothermal fluid properties,thermal fluid eco-system and hydrothermal product indicate that there is possibly another injected circulation pattern for modern seafloor hydro-thermal systems,which means the hydrothermal fluid is derived from the direct injection of fluid and volatile components from the deep magma chamber.Accordingly,it is inferred that there possibly are two models for modern seafloor hydrothermal sys-tems:one is the shallow circulation mode,namely the traditional mode of hydrothermal circulation;the other is a magmatic hy-drothermal injection mode("injection model").In the environment of strong magmatism and well-developed fracture,two modes may exist simultaneously,and the double diffusive convection circulation model is proposed.The double diffusive con-vection circulation model can be used to explain a variety of phenomena and facts recently discovered in the study of modern seafloor hydrothermal system.Moreover,it is pointed out that the tectonic background of the subduction and the mixing of ma-terials from both subduction component and continental crust are also considered in the study of the magmatism and hydrother-mal activity in back-arc basin.Meanwhile,a theoretical model has been constructed for the sea-floor hydrothermal system in back-arc basin taking the Okinawa trough as an example.