Geochemical Characteristics of Surface Sediments in the Xunmei Hydrothermal Field (26°S), Mid-Atlantic Ridge: Implications for Hydrothermal Activity

Abstract

The compositions of metalliferous sediments which is associated with hydrothermal vents can provide reliable geochemical indicators for the exploration of seafloor sulfides. In this study, surface sediments from the Xunmei hydrothermal field (HF) on the South Mid-Atlantic Ridge (SMAR) were selected, and their major and trace elements were analysed. The results showed that the sediments are composed of pelagic material (calcium biogenic components), basaltic debris, iron-manganese oxides, and a mixture of hydrothermal components. Additionally, the sediments were found to be significantly enriched in Cu, Zn, Fe and Co derived from hydrothermal sources, as well as Mn, V, Mo, U and P, which are primarily scavenged from seawater. The Cu and Zn concentrations are highest in the northeastern part of Xunmei, while the northeastern, northern, and southern parts are characterized by great inputs of hydrothermal Fe. Manganese and Mo are mainly enriched in the western and southern parts and show a strong positive correlation, indicating that Mo is mainly scavenged by Mn oxides. There are high positive correlations among U, P, and Fe, indicating their coprecipitation with Fe from hydrothermal plumes. Vanadium and Co are introduced into sediments in two ways, i.e., V is scavenged and coprecipitates from hydrothermal plumes, and Co is derived from sulfide debris. Based on the variations in Cu and Zn contents and in the Cu/Fe (0.159), Zn/Fe (0.158), and Fe/Mn (1440) ratios, it can be inferred that a high-temperature hydrothermal vent existed in northeastern Xunmei. In combination with the distribution patterns of the above elements, the hydrothermal vents in the southern part ceased erupting after a short period of activity. In addition, the high Mn anomaly and the high U/Fe ratios at the boundaries of the investigated area indicate the presence of a relatively oxidized environment in southwestern Xunmei.