10:15 AM - 10:30 AM
[SCG55-17] Distribution of submarine volcanoes in the Tokara Islands, Kagoshima Prefecture, Japan: Relation to stretching field due to rifting of the back-arc basin
Keywords:Tokara Islands, Submarine volcano, Island arc-trench system, Okinawa Trough, Arc-parallel extension, Cross-arc volcanism
The Okinawa Trough, which is considered to be in the early stage of back-arc basin, is expected to provide clues regarding the beginning of back-arc rifting, and this will contribute to the understanding of the relationship between the back-arc rifting process and the tectonic controls on volcanic activity. The Tokara Islands, located in the northeast of the Okinawa Trough, Japan. These volcanic islands form part of the volcanic front aligned in NNE-SSW direction associated with the subduction of the Ryukyu Trench. In addition, to this region’s west, seamounts are densely distributed in the WNW-ESE direction. These complexly aligned volcanic edifices can provide key information on the volcanic activity in the early stage of the development of the Okinawa Trough. However, a systematic understanding of the spatiotemporal variations in the magmatic activity is limited.
In this study, we identified submarine volcanoes based on the seismic profile obtained from the multichannel seismic reflection survey in order to first organize the spatial information of volcanic activity in this sea area. This study shows that submarine volcanoes are aligned in two distinct directions. In addition, in this study, we compared the direction of these volcanic lines with the orientation of lineaments and found that they have two same directions. The orientation of lineaments is referred to Ishino et al. (2022, 2023). These arrays are named VA1 and VA2, respectively.
VA1 is distributed in ENE-WSW (including Yokoate Echelon Knoll Chain). Around this volcanic array, there are a group of lineaments with the same orientation which are often seen around the eastern margin of Okinawa Trough. VA2 aligned in WNW-ESE. This VA2 includes two volcanic belts, the northern one and the southern one. The two belts extend to WNW, the northern one from Kodakarajima Island, and the southern one from Yokoatejima Island, respectively. Both reach near the eastern margin of the Okinawa Trough. On the forearc side of VA2, a group of lineaments with similar direction is recognized corresponding to the northern array and the southern array, respectively.
The above relationship between volcanic array and lineaments suggests that fracture zone in the crust or faults with trends similar to those of VA1 and VA2 were possibly used as pathways for magma. This indicates that the following mechanism: the VA1 was formed in relation to NNW-SSE extension (arc-perpendicular extension) and the VA2 was constructed by NE-SW extension (arc-parallel extension). The previous study suggests that such a two directional stretching stress field is formed in association with the rifting of a curved island arc (Koge et al., 2024). Therefore, the results of this study indicate that 2 directional extension fields associated with the rifting of the Okinawa Trough play an important role in volcanism in the northern Ryukyu Arc.
[Ishino, S., Misawa, A., Arimoto, J., Inoue, T., 2022. Seismic survey of GB21-1 Cruise off southwest Tokara Islands. Bull. Geol. Surv. Jpn. 73(5/6), 219-234.]
[Ishino, S., Harigane, Y., Misawa, A., Inoue, T., 2023. Overview of the seismic survey and dredge sampling in the vicinity of the Tokara Islands conducted during geological map research cruise in 2021. Bull. Geol. Surv. Jpn. 74(5/6), 211-230]
[Koge, H., Sato, T., Arimoto, J., Otsubo, M., Ishino, S., Suzuki, Y., Ishizuka, O., Harigane, Y., Misawa, A., Inoue, T., Yamashita, M., Furuyama, S., Yokoyama, Y., Sato, Y., Mori, T., Minami, H., Tamura, C., 2024. Inception of ridge-ridge-ridge triple junction: Morphostructural analysis and dynamics in the early back-arc extension of the northern Okinawa Trough. Geology. ]
In this study, we identified submarine volcanoes based on the seismic profile obtained from the multichannel seismic reflection survey in order to first organize the spatial information of volcanic activity in this sea area. This study shows that submarine volcanoes are aligned in two distinct directions. In addition, in this study, we compared the direction of these volcanic lines with the orientation of lineaments and found that they have two same directions. The orientation of lineaments is referred to Ishino et al. (2022, 2023). These arrays are named VA1 and VA2, respectively.
VA1 is distributed in ENE-WSW (including Yokoate Echelon Knoll Chain). Around this volcanic array, there are a group of lineaments with the same orientation which are often seen around the eastern margin of Okinawa Trough. VA2 aligned in WNW-ESE. This VA2 includes two volcanic belts, the northern one and the southern one. The two belts extend to WNW, the northern one from Kodakarajima Island, and the southern one from Yokoatejima Island, respectively. Both reach near the eastern margin of the Okinawa Trough. On the forearc side of VA2, a group of lineaments with similar direction is recognized corresponding to the northern array and the southern array, respectively.
The above relationship between volcanic array and lineaments suggests that fracture zone in the crust or faults with trends similar to those of VA1 and VA2 were possibly used as pathways for magma. This indicates that the following mechanism: the VA1 was formed in relation to NNW-SSE extension (arc-perpendicular extension) and the VA2 was constructed by NE-SW extension (arc-parallel extension). The previous study suggests that such a two directional stretching stress field is formed in association with the rifting of a curved island arc (Koge et al., 2024). Therefore, the results of this study indicate that 2 directional extension fields associated with the rifting of the Okinawa Trough play an important role in volcanism in the northern Ryukyu Arc.
[Ishino, S., Misawa, A., Arimoto, J., Inoue, T., 2022. Seismic survey of GB21-1 Cruise off southwest Tokara Islands. Bull. Geol. Surv. Jpn. 73(5/6), 219-234.]
[Ishino, S., Harigane, Y., Misawa, A., Inoue, T., 2023. Overview of the seismic survey and dredge sampling in the vicinity of the Tokara Islands conducted during geological map research cruise in 2021. Bull. Geol. Surv. Jpn. 74(5/6), 211-230]
[Koge, H., Sato, T., Arimoto, J., Otsubo, M., Ishino, S., Suzuki, Y., Ishizuka, O., Harigane, Y., Misawa, A., Inoue, T., Yamashita, M., Furuyama, S., Yokoyama, Y., Sato, Y., Mori, T., Minami, H., Tamura, C., 2024. Inception of ridge-ridge-ridge triple junction: Morphostructural analysis and dynamics in the early back-arc extension of the northern Okinawa Trough. Geology. ]