[S-GL23] Geologic structure and tectonic history of East Asia and Japanese Islands

[SGL23-P07] Granitic rocks exposed at the seafloor around the Goto Islands, the westernmost Kyusyu, Japan

*Tomo Aoki¹, Osamu Ishizuka², Yumiko Harigane² (1.Japan Coast Guard, 2.AIST)

Keywords:East China Sea, Okinawa Trough, Japan Sea, granite

Granitic rocks occurring in the westernmost Japan Archipelago, such as the Goto Islands, are considered to be formed associated with the formation of the Japan Sea and the northernmost Okinawa Trough (e.g., Kiyokawa et al., 2022). These magmatic processes forming granitic rocks are important for understanding the Miocene volcanism in the southwestern Japan. Tokuyama et al. (2001) reported that the seafloor of southern side of the Goto Islands widely consists of basement rocks. However, only a few studies based on lithological and geochemical data from seafloor samples exist.
The Japan Coast Guard conducted geological survey and collected granitic rocks from several dredged sites in this area. Recently, Aoki et al. (2024) suggested that the granitic rocks dredged from the seafloor nearby the Hizen-Tori Shima Island are comparable with the granitic rock from the Goto Islands. In this presentation, we present the detailed lithological and geochemical data of the granitic rocks dredged from the seafloor around the Goto Islands. We would like to discuss their spatial distributions and geochemical characteristics by using their whole-rock major and trace element compositions and K-Ar dating.

References:
[1] Kiyokawa et al. (2022) Island Arc 31(1), e12456.
[2] Tokuyama et al. (2001) Journal of the Japan Society for Marine Surveys and Technology, 27-53.
[3] Aoki et al. (2024) 131th The Geological Society of Japan.