The Gondou hydrothermal field in the Ryukyu Arc: A huge hydrothermal system on the flank of a caldera volcano

Abstract

High‐resolution geophysical mapping was conducted from an autonomous underwater vehicle on the flank of Daisan‐Kume Knoll in the Ryukyu Arc, southwest of Japan. 1 m resolution bathymetry identified 264 spires, 173 large mounds and 268 small mounds within a depression that is up to 1600 m wide and up to 60 m deep, at water depths between 1330 and 1470 m. Hydrothermal venting is strongly inferred from the observation of plumes in sidescan sonar imagery and positive temperature anomalies over the spires and mounds. This field, named the Gondou Field, has a giant mound G1 with a diameter of 280 m and a height of 80 m. Mound G1 has distinctive summit ridges composed of multiple spires where acoustic plumes with temperature anomalies up to 1.12°C are observed, indicative of high‐temperature venting. Other than mound G1, a number of active large mounds more than 30 m wide and spires over 10–22 m tall are common and they concentrate in the central and southern areas of the field, suggesting that these areas are the center of present hydrothermal activity. Acoustic plumes imaged by side‐scan sonar at the Gondou Field are different in character from bubble plumes imaged in other hydrothermal fields in the Ryukyu Arc. The plumes are diffused and deflected as they rise through the water column and have a shape consistent with black smokers.

Seismic structure of rifting in the Okinawa Trough, an active backarc basin of the Ryukyu (Nansei-Shoto) island arc–trench system

“…The slope at the northern margin of the southern OT shows a steeper gradient than that in the northern OT and is cut by submarine channels of varying size. Over ten hydrothermal vents have been found through the OT, and some of them have been investigated in great detail (e.g., Beaulieu 2015;Ishibashi et al 2015;Minami and Ohara 2017). However, a volcanic front is recognizable only to the west of the Ryukyu Arc in the northern and middle OT, but not in the southern OT.…”

Visual and Autonomous Survey of Hydrothermal Vents Using a Hovering‐Type AUV: Launching Hobalin Into the Western Offshore of Kumejima Island

“…This site is located in the western offshore of Kumejima Island, which is approximately 100 km west of Okinawa Main Island. In 2014, the Japan Coast Guard conducted acoustic bathymetric surveys using the cruising AUV Gondou at altitudes of 50–70 m and confirmed that myriads of chimneys and mounds exist (Minami and Ohara, ). In 2015 and 2016, the Japan Agency for Marine‐Earth Science and Technology also conducted surveys using the cruising AUV Urashima (Kitada et al, ; Nakamura, ) and the HOV Shinkai 6500 (Kasaya, ), respectively.…”

“…Chimney structures are typically formed in the seafloor of hydrothermal vent fields and can grow to a height of several tens of meters (Nozaki et al, ; Minami and Ohara, ; Tivey, ). To avoid collision with these structures, Hobalin has an obstacle avoidance system consisting of several devices such as forward‐ and downward‐looking cameras, line lasers, and thermometers (Okamoto, Tamura, et al, ; Okamoto et al, ).…”

Pseudo-3D seismic imaging of Geolin Mounds hydrothermal field in the Southern Okinawa Trough offshore NE Taiwan

“…Hydrothermal activities usually occur along with submarine edifices (e.g., volcanos, mounds and chimneys) and are rich in mineral deposits, reflecting subsurface and active hydrothermal circulation. The formation and evolution of hydrothermal fields are regionally controlled by tectonics such as plate subduction and associated rifting, and are locally controlled by magma activities, host rocks composition, segregation process as well as fluid migration (Von Damm 1990;Charlou et al 1996;Tivey 2007;Kelley et al 2012;Minami and Ohara 2017). For last decade, the potential of marine mineral resources in hydrothermal fields enriched by hydrothermal circulation that expedite chemical exchanges between hydrothermal fluid and its surrounding crust is receiving increasing attention, especially in the Okinawa Trough (e.g., Inagaki et al 2006;Ishibashi et al 2015;Nozaki et al 2016;Toki et al 2016;Minami and Ohara 2017), which is a back-arc basin at rear side of the Ryukyu arctrench system along the tectonic boundary between the Eurasian Plate and subducting Philippine Sea Plate (Lee et al 1980;Letouzey and Kimura 1986;Sibuet et al 1987Sibuet et al , 1998.…”