The axial valley morphology and related hydrothermal activities at the Central Spreading Ridge, the North Fiji Basin

Abstract

Korea Institute of Ocean Science and Technology (KIOST) has conducted an expedition to delineate distribution patterns of seafloor massive sulfides and its geotectonic background over a spreading ridge (Central Spreading Ridge CSR) and a triple junction in North Fiji Basin for 52 days from 23 October to 13 December 2016. Based on the previous surveys, the exploration concentrated on the KF 2 and KF3 regions that had shown the high chance of seafloor hydrothermal activity among the three regional sites (KF 1, KF 2 and KF 3) in Fijian EEZ. KF2 is situated next triple junction to the south and KF3 is located along spreading center at the southern part of the CSR. High-resolution mappings over the KF2 reveal the high land that probably formed by the mass eruption of basaltic lava and the abyssal hills by tectonic extension, resulting in graben structure. The very next region of the triple junction is featured by pit crater of approximately 1.8 km in diameter. The pit crater is likely to be formed by disruption of the large basalt tube. The clear boundary of a crater and abyssal-hill fabric and their connectivity to the outer part of crater indicate the crater was developed after tectonic extension. Whereas the obvious abyssal hill fabric in KF3 is rarely traced but NS-trending lineaments are well observed instead, which corresponds to a set of fracture zones. The NS-trending fractures are characterized by a pull-apart riple junction in North Fiji Basin for 52 days from 23 October to 13 December 2016. Based on the previous surveys, the exploration concentrated on the KF 2 and KF3 regions that had shown the high chance of seafloor hydrothermal activity among the three regional sites (KF 1, KF 2 and KF 3) in Fijian EEZ. KF2 is situated next triple junction to the south and KF3 is located along spreading center at the southern part of the CSR. High-resolution mappings over the KF2 reveal the high land that probably formed by the mass eruption of basaltic lava and the abyssal hills by tectonic extension, resulting in graben structure. The very next region of the triple junction is featured by pit crater of approximately 1.8 km in diameter. The pit crater is likely to be formed by disruption of the large basalt tube. The clear boundary of a crater and abyssal-hill fabric and their connectivity to the outer part of crater indicate the crater was developed after tectonic extension. Whereas the obvious abyssal hill fabric in KF3 is rarely traced but NS-trending lineaments are well observed instead, which corresponds to a set of fracture zones. The NS-trending fractures are characterized by a pull-apart