Hydrothermal fluid flow system around the Iheya North Knoll in the mid-Okinawa trough based on seismic reflection data

Seismic reflection data around the Iheya North Knoll hydrothermal field provide insights into geological structures that control subseafloor hydrothermal fluid flow in the sediment-covered continental backarc basin of the mid-Okinawa Trough. We identified the seismic expression of widespread porous volcaniclastic pumiceous deposits and intrusions as a result of silicic arc volcanism. The porous and permeable volcanic deposits are distributed in an area extending updip from the thick succession of the deep trough to the seafloor at the hydrothermal field. Their regional structure focuses the flow of hydrothermal fluids derived from the surrounding trough-fill sediments and directs them to the vents of the hydrothermal field. The high concentrations of CH4 and NH4 in the fluids of the hydrothermal field are likely derived from the interaction of migrating fluids with trough-fill sediments.

► Possible fluid flow paths in the Iheya North Knoll hydrothermal field.
► Widespread permeable volcanic deposits produced by silicic arc volcanism.
► Layered sequence focuses migration of fluids derived from trough-fill sediments.
► Fluid alteration accelerated by interactions with sediments.