[S-CG45] 海洋底地球科学

[SCG45-P14] 沖縄トラフ伊江山熱水域から得られた堆積物コアの鉱物学的・地球化学的研究

*石橋 純一郎¹、宮本 尭^1,3、戸塚 修平^1,2、島田 和彦¹、山崎 徹²、池原 研²、長瀬 敏郎⁴、高谷 雄太郎⁵、町山 栄章⁶、飯島 耕一⁶、山本 浩文⁶、熊谷 英憲⁶ (1.九州大学理学部地球惑星科学科、2.産業技術総合研究所、3.東京大学大学院理学系研究科、4.東北大学総合学術博物館、5.早稲田大学理工学術院総合研究所、6.海洋研究開発機構)

キーワード：海底熱水鉱床、鉱化作用、熱水域海底下、BMS掘削

Ieyama hydrothermal field is located at the seafloor around a water depth of 1050-1100 mbsl (meters below the sea level) in the mid-Okinawa Trough. Semi-detailed exploration survey during YK17-18C cruise using AUV (Autonomous underwater vehicle) identified negative self-potential anomalies probably related to mineralization on and beneath the seafloor in this area (Kasaya et al., 2020). Moreover, ROV (Remotely operated vehicle) surveys conducted in the same and later durations observed and accessed present hydrothermal activities represented by high temperature fluid venting from mound structure consisted of sulfide and sulfate mineral deposits. Scientific drilling was performed by J-MARES during the SIP Integrated Ocean Resource Surveying System JM18-04 Cruise in September 2018. Sediment cores were obtained from 3 sites in the Ieyama field, employing BMS (Boring Machine System) installed on Shincho-maru. Lithology and mineralogy of the obtained sediment cores were studied based on VCD (Visual Core Description), measurements of physical properties, XRD (X-ray diffractometer) analysis, and electron probe microanalyzer (EPMA) analysis.

Sulfide mineralization was recognized in the layer from 50 to 65 mbsf (meters below the seafloor) of the sediment core collected from a bottom of circular depression of about 100 m diameter. This layer was overlaid by thick pile of pumice and pumiceous tuff, and underlaid by tuffaceous breccia. Mineralogical and chemical studies of sulfide minerals revealed several similarities to sulfide minerals collected from chimney and mound structures found in the vicinity of the drilled site.

Acknowledgements:

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 CSTI, Cabinet Office, Government of Japan. We are thankful to J-MARES (Research and Development Partnership for Next Generation Technology of Marine Resources Survey) for providing samples used in this study.