Numerical simulation-based clarification of a fluid-flow system in a
seafloor hydrothermal vent area in the middle Okinawa Trough
Abstract
Despite many studies on seafloor hydrothermal systems conducted to date,
the generation mechanism of seafloor massive sulfide (SMS) deposits is
not yet fully understood. To elucidate this mechanism, this study
clarifies the three-dimensional regional temperature distribution and
fluid flow of a seafloor hydrothermal system of the Iheya North, middle
Okinawa Trough. Lateral flow and boiling of hydrothermal fluids below
the seafloor were the main features found by the simulation, leading to
an interpretation of two-layered SMS deposit generation as follows.
Hydrothermal fluids discharging from black smokers first formed the
upper SMS deposits on the seafloor. Caprocks formed below the seafloor,
and the above-mentioned occurrences were then induced under the
caprocks. In the present system, vapor-rich hydrothermal fluids poor in
metals are discharged from the vents as white smokers, whereas
liquid-dominated hydrothermal fluids rich in metals flow laterally below
the caprocks, forming lower SMS deposits tens of meters below the
seafloor.