Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG56] Ocean Floor Geosciences

Mon. May 27, 2019 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Kyoko Okino(Atmosphere and Ocean Research Institute, The University of Tokyo)

[SCG56-P13] Mineralogical and geochemical study of sediment cores collected from the Gondou hydrothermal field in the Okinawa Trough

*Jun-ichiro Ishibashi1,2, Shuhei Totsuka2, Akihi Tsutsumi2, Naru Tsukamoto2, Yusuke Kira2, Kazuhiko Shimada1, Toru Yamasaki3, Ken Ikehara3, Toshiro Nagase4, Yutaro Takaya5,9, Kei Ikehata6, Takashi Goto7, Chitaro Gouzu7, Ryuichi Shinjo8, Hideaki Machiyama9, Koichi Iijima9, Hirofumi Yamamoto9, Hidenori Kumagai9 (1.Department of Earth and Planetary Sciences, Kyushu University, 2.Graduate School of Science, Kyushu University, 3.National Institute of Advanced Industrial Science and Technology, 4.Tohoku University Museum, 5.School of Creative Science and Enginerring, Waseda University, 6.Faculty of Life and Environmental Sciences, University of Tsukuba, 7.Hiruzen Institute for Geology and Chronology, 8.Faculty of Science, University of the Ryukyus, 9.Japan Agency for Marine-Earth Science and Technology)

Keywords:seafloor massive sulfide deposits, seafloor scientific drilling, hydrothermal alteration

Intense hydrothermal activity associated with sulfide mineralization had been observed in the Gondou field, which is located at the seafloor around a water depth of 1330-1470 mbsl (meters below the sea level) at the western flank of the Daisan-Kume Knoll (Minami and Ohara, 2017; Ishikawaet al., 2016). Scientific drilling was performed by J-MARES during the SIP Integrated Ocean Resource Surveying System JM17-04 Cruise from October to November, 2017. Sediment cores were obtained from 5 sites in Southern area of the Gondou field by drilling using BMS (Benthic Multi-coring System) installed on Shincho-maru. Mineralogy and geochemistry of the obtained cores were studied based on VCD (Visual Core Description), microscopic observation, XRD (X-ray diffractometer) analysis, and electron probe microanalyzer (EPMA) analysis.
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).