Geochemical Assessment on Hydrothermal Contribution to Floor Sediments from the Kita-Bayonnaise Submarine Caldera, Izu-Ogasawara Arc, Northwestern Pacific

摘要

A geochemical study of sediment and rock samples was conducted in the Kita-Bayonnaise submarine caldera, Shichito-Iwojima Ridge, Izu-Ogasawara Arc, northwestern Pacific, in order to assess hydrothermal contributions to caldera sediments. The caldera is covered mainly with ash to cobble-sized pumice, and its wall consists of pumice and rhyolitic lava flows. The amounts of Au, Ag, Zn, Pb, Cu, Ba, Sb, As, and Cd in the caldera floor sediments are extremely high relative to those in the volcanic rocks that comprise the caldera wall. The sediments enriched in these elements usually contain varying amounts of sulfides, fahlerz, and barite. R-mode factor analysis of element abundances reveals three major factors that explain most of the chemical variation: sulfides and barite, Mn-oxyhydroxides, and detrital Fe-bearing minerals. The high factor scores of the eastern floor samples represent sulfides-barite mineralization with Au and, Ag enrichments, while those of the western floor samples signify both Mn-oxyhydroxide and sulfides-barite mineralization.