[SCG56-P13] Mineralogical and geochemical study of sediment cores collected from the Gondou hydrothermal field in the Okinawa Trough
Keywords:seafloor massive sulfide deposits, seafloor scientific drilling, hydrothermal alteration
Most part of the obtained sediment, except for the surface hemipelagic sediment within a few mbsf (meters below the seafloor), was hydrothermally altered intensely. Abundant occurrence of illite (or illite/smectite mixed-layer mineral) was observed, which is common signature among hydrothermal alteration in hydrothermal fields in the Okinawa Trough. Whereas, occurrence of chlorite was limitedly recognized within a layer of 5-15 m thickness in each site. Kaolin minerals were identified in altered pumiceous volcaniclastic sediment in two sites. These specific occurrences may reflect subseafloor fluid migration of distinctive chemistry, based on the idea that chlorite formation would be related to interaction with heated seater-derived fluid while kaolin minerals formation would be related to interaction with acidic fluid. Occurrence of sulfate minerals such as anhydrite and barite is also limited, which may provide another information about subseafloor fluid migration.
This study was conducted under the framework of the Next-Generation Technology for Ocean Resources Exploration Project, Cross-ministerial Strategic Innovation Promotion Program (SIP) funded by the Japanese cabinet office. The sediment cores used in this study were provided from J-MARES (Research and Development Partnership for Next Generation Technology of Marine Resources Survey).