[S-CG48] 海洋底地球科学

[SCG48-P07] Characteristics of Deposits in the Southern Okinawa Trough: Preliminary Report of Cruise KH-23-11

桑野 太輔¹、*藤島 誠也¹、池原 実²、オブラクタ スティーブン³、大坪 誠⁴、木下 正高⁵、KH-23-11 乗船研究者一同 (1.京都大学、2.高知大学海洋コア国際研究所、3.秋田大学大学院国際資源学研究科、4.産業技術総合研究所、5.東京大学地震研究所)

キーワード：沖縄トラフ、背弧海盆、混濁流、タービダイト

The Okinawa Trough is currently an active back-arc basin, representing an early stage of continental crustal thinning characterized by intermittent rifting since approximately 2 million years ago. However, the mechanisms driving crustal thinning at this stage remain unclear. In order to elucidate these processes, comprehensive marine geoscientific observations were conducted during cruise KH-23-11 of the R/V Hakuho-maru from December 2023 to January 2024. This study focuses on the lithology and accumulation rate of sediments that infilled the axial portion of the back-arc basin during the early stages of development. During the cruise, heat flow piston coring and long-piston coring were conducted at eight sites. Several cores were split on board and then imaged using the Namahage core image scanner prior to color and thermal conductivity measurements. Finally, the archive halves of the split cores were and visually described and the working halves were samples. On shore, the cores were imaged by the CT scanner at the Marine Core Research Institute, Kochi University. Sediments primarily consist of homogenous clay to silt and well-sorted clay interspersed with very fine to medium sand, suggesting that sediment transport to the southern Okinawa Trough is predominated by turbidity currents originating from Taiwan, as well as hemipelagic sediment deposition. Future research will aim to estimate sedimentation rates, which is expected to elucidate the relationship between heat flow, interstitial water composition, and sedimentary systems.