Figure F6. Subseafloor structure of the hydrothermal field and the central valley of Iheya North based on the profile of multichannel seismic Line MCS18. Expedition 331 drilling sites and total drilled depths tentatively converted to two-way traveltime are shown as blue bars, along with a possible hydrogeologic interpretation assuming that 1 s of two-way traveltime corresponds to 750 m. Black and gray blank diamonds show the upper and lower reflections of potential pyroclastic flow deposits beneath the central valley of Iheya North Knoll. These volcanic deposits are possible subseafloor hydrothermal migration paths. In contrast, black and gray blank circles show the upper and lower bounds of negatively polarized reflection sequences beneath the western hill structure near the vent sites. These negative polarity sequences are presently interpreted as very porous, fractured deposits that may host a hydrothermal reservoir and fluid migration paths.
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