[M-ZZ44] Marine Manganese Minerals: Depositional environments, exploration, and development

[MZZ44-P03] Occurrence, composition, microstructure and growth age of the ferromanganese crusts in the Minami Seamount, the Ogasawara Plateau

*Akira Usui¹, Tsubasa Kamei², Murayama Masafumi¹, Takeyasu Yamagata³, Hiroyuki Matsuzaki³, Ayumu Onda⁴ (1.Marine Core Research Institute, Kochi University, 2.Fac. Agriculture & Marine Sciences, Kochi University, 3.The University Museum, The University of Tokyo, 4.Fac. Science and Technology, Kochi University)

Keywords:Ogasawara Plateau, ferromanganese crust, ROV, microstrutigraphy

The hydrogenetic ferromanganese deposits were observed and collected using the ROV/JAMSTEC HyperDolphin (ROV) along 5-km survey lines near the flat tops and the slopes over the Minami Seamount, the Ogasawara Plateau, located 200 km east off the Chichijima, Islands. The collected crust samples were regarded as long-range sediment cores, and microstratigraphically described, and categorized as a type of “Pacific-Plate group,” which are typical in the eastern part of the area (from Minamitori Island to the Marcus Islands). The deposits are characterized by a clear two-layer boundary, probably dating back to the Paleogene, and significant change in mineral and chemical composition at the layers. The tectonic setting of the area is unique to huge plateau (+ seamounts) colliding towards the island arc, with the active tectonic lines and faults in the surrounding area, so the crusts growing in the area may incorporate debris particles supplied from seamounts or island arcs, and the higher growth rate (based on Be isotopic ages) and structure of the crusts are also peculiar to the active areas.