[S-CG48] Ocean Floor Geoscience

[SCG48-16] Marine and earth science surveys in the Southern part of Okinawa Trough: Hakuho-maru KH-23-11 cruise preliminary reports

*Makoto Otsubo¹, Masataka Kinoshita², Minoru Ikehara³, Ryuta Arai⁴, Ayanori Misawa¹, Hiroaki Koge¹, Katsura Kameo⁵, Chiori Tamura⁵, Ryoji Toda⁵, Stephen P. Obrochta⁶, Takanori Kagoshima⁷, Tomohiro Toki⁸, Daisuke Kuwano⁹, Seiya Fujishima⁹, Akane Yamamoto^1,10, Natsuki Nomura¹¹, Aya Osanai¹¹, Keita Kono¹¹, Issui Ikuma¹¹, Chika Onai¹², Yusei Miyamoto¹², Yuka Taira⁸, Yu Miyagi⁸, Soma Sato⁶, Michelle M. Nishimoto^13,1, Yukihiko Nakano¹⁴, Hikaru Iwamaru¹⁵, Yu Suzuki¹⁶ (1.Geological Survey of Japan, AIST, 2.ERI, The University of Tokyo, 3.Marine Core Research Institute, Kochi University, 4.JAMSTEC, 5.AORI, The University of Tokyo, 6.Akita University, 7.Toyama University, 8.The University of Ryukyus, 9.Kyoto University, 10.Nihon University, 11.Kochi University, 12.Chiba University, 13.Japan Women's University, 14.Marine Works Japan Ltd., 15.Nippon Marine Enterprises, Ltd., 16.MOL Marine & Engineering Co., Ltd.)

Keywords:Okinawa Trough, Backarc basin, Normal fault, Ryukyu arc, Scientific Drilling

As a preliminary report, this presentation provides an overview of the Hakuho-maru KH-23-11 cruise in the southern part of Okinawa Trough, which was conducted from December 28th, 2023 to January 11th, 2024. The Okinawa Trough (East China Sea) is a back-arc basin located on the Eurasian Plate and is an early stage of thinning of the continental crust, which has been undergoing intermittent spreading (rifting) for 2 million years. It is not clear how the crust thins during this stage and what factors promote this thinning. In this study, we focused on the possibility of crustal weakening caused by fluid migration and thermal condition along faults in the early stage of back-arc basin development, and conducted seismic reflection surveys and bathymetric surveys over a wide area, focusing on the Yaeyama and Yonaguni rifts in the southern part of the Okinawa Trough, where the spreading is most advanced, and conducted seismic reflection surveys at several locations in the two rifts. In the KH-23-11 Cruse, at several points in both rifts, we collected sediments filling the Okinawa Troughs by piston coring, extract water and gas from the collected sediments, measure crustal heat flow around the trough axes, and conduct water sampling and CTD observations.

Acknowledgments: We would like to express our sincere gratitude to the Operation Department of the Japan Agency for Marine-Earth Science and Technology, the staff of the Atmosphere and Ocean Research Institute of the University of Tokyo, and the crew of the Hakuho-maru for their hard work in making this cruise possible.