Geochemical characteristics of hydrothermal sediments from Iheya North Knoll in the Okinawa Trough

Thirty sediment subsamples were recovered from the Iheya North hydrothermal field (with an average of 38 m away from the hydrothermal vent) in the middle Okinawa Trough. Samples were obtained by the ROV (Remote Operated Vehicle) Faxian during the virgin cruise of the R/V Kexue in 2014 with the application of push cores. The chemical compositions of the sediments show that the hydrothermal sediments near the hydrothermal vent are mainly composed of SO3, ZnO and Fe2O3. Moreover, the hydrothermal sediments are also highly enriched in Pb, As, Sb, Hg, Se, Ag, Ba, Mo and Cd comparing with previous analysis results. On the other hand, the concentrations of Sr, Hg and Ag in studied sediments are strongly and positively correlated, these elements can be used as an hydrothermal indicator. In addition, a factor analysis of the sediments suggested that the sediments were mainly influenced by hydrothermal origin, and terrestrial and biogenic input are limited in studied area. It is also suggested that different stages of crystallization were involved in the formation of hydrothermal chimney from factor analysis.