Petrological features from volcanic rocks around the Daisan-Miyako Knoll in the Central-Southern Ryukyu Arc

抄録

The Ryukyu Arc is situated between the islands of Kyushu and Taiwan (~1200 km in the full length). This arc is formed by subduction of the Philippine Sea plate beneath the Eurasia Plate along the Ryukyu trench, and is composed of forearc islands, chains of arc volcanoes, and a back-arc rift called Okinawa Trough. Ryukyu Arc is commonly divided into three segments (northern, central and southern) that bounded by the Tokara Strait and the Kerama Gap, respectively (e.g., Konishi, 1965; Kato et al., 1982). The northern Ryukyu Arc (i.e., the Tokara Islands) has more numerous active frontal arc volcanoes occurred at both of subaerial and submarine fields. However, there are sparse active submarine volcanoes related to frontal arc volcanism from the southwest of Iotori-shima in the central-southern Ryukyu Arc (Kimura et al., 1986; Shinjo et al., 1999). In addition, the volcanic activities related to back-arc rifting of the Okinawa Trough well-develop around the central-southern Ryukyu Arc. The existence of volcanic activity associated with volcanic front developed in the central-southern Ryukyu Arc and their petrological characteristics, magmatic features, and contribution of slab-derived materials are still unknown due to few geological surveys and studies.In 2021, detailed geophysical and geological investigation around the Daisan-Miyako Knoll, the Ikema Knoll and the Daiichi-Miyako Knoll was undertaken by KS-21-16 cruise based on the detail morphological data reported from Minami and Ohara (2018). In this presentation, we present the cruise summary of the KS-21-16 and preliminary petrological and geochemical data for these submarine volcanoes.

References:

Kato, S., Katsura, T., Hirano, K., 1982. Submarine geology off Okinawa Island. Report of Hydrographic and Oceanographic Researches, 17, 31–70 (in Japanese with English abstract).

Kimura, M., Kaneoka, I., Kato, Y., Yamamoto, S., Kushiro, I., Tokuyama, H., Kinoshita, H., Isezaki, N., Masaki, H., Oshida, A., Uyeda, S., Hilde, T. W., 1986. Report on DELP 1984 Cruises in the Middle Okinawa Trough. V: Topography and geology of the central grabens and their vicinity. Bulletin of the Earthquake Research Institute, University of Tokyo, 61, 2, 269-310.

Konishi, K., 1965. Geotectonic framework of the Ryukyu Islands (Nansei-Shoto). Journal of the Geological Society of Japan, 71, 437–457 (in Japanese with English abstract).

Minami, H., & Ohara, Y., 2018. Detailed volcanic morphology of Daisan-Miyako Knoll in the southern Ryukyu Arc. Marine Geology, 404, 97-110.

Shinjo, R., Chung, S. L., Kato, Y., Kimura, M., 1999. Geochemical and Sr-Nd isotopic characteristics of volcanic rocks from the Okinawa Trough and Ryukyu Arc: Implications for the evolution of a young, intracontinental back arc basin. Journal of Geophysical Research, 104, B5, 10591-10608.