[S-CG48] Ocean Floor Geoscience

[SCG48-18] Inception of Ridge-Ridge-Ridge Triple Junctions: Geomorphological Evidence and Tectonic Dynamics in the Early Back-Arc Extension of the Northern Okinawa Trough

*Hiroaki Koge¹, Taichi Sato¹, Jun Arimoto¹, Makoto Otsubo¹, Saki Ishino¹, Yoshiaki Suzuki¹, Osamu Ishizuka¹, Takahiko Inoue¹, Mikiya Yamashita¹, Seishiro Furuyama², Yuka Yokoyama³, Hiroki Minami⁴, Chiori Tamura⁵ (1.Geological Survey of Japan, AIST, 2.Tokyo University of Marine Science and Technology, 3.Tokai University, 4.Japan Coast Guard, 5.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:Okinawa Trough, Back-arc spreading , Triple junction

Ridge-Ridge-Ridge (RRR) triple junctions are pivotal phenomena associated with plate boundary dynamics and crustal extension, yet their formation mechanisms and evolution are not fully elucidated. This study analyzes the tectonics in the initial stages of back-arc extension through a detailed seabed morphological survey of the Northern Okinawa Trough, providing insights into the potential development of RRR triple junctions in the future. Detailed analysis through bathymetry indicates the presence of pronounced lineament structures identified as fault structures by seismic profiles, suggesting their origination from a consistent stress field oriented in an approximately north-south extensional direction. Specifically, the Okinawa Trough, Tokara Gap, and the newly identified Yokoate Echelon Knoll Chains were formed under this consistent stress field, with the potential for ongoing activity revealed through k-means clustering analysis and stress tensor inversion methods. This north-south extensional stress field coincides with the dominant stress field on the southern side of the Okinawa Trough, implying that continued back-arc extension, progressing from rifting to spreading, could lead to the formation of RRR triple junctions. These findings represent a significant step toward elucidating the formation process of RRR triple junctions and promote understanding of plate interactions within a broader geotectonic context.