Geochemical Profiles of Three Deep-sea Hydrothermal Plumes of the Eastern Lau Spreading Center

Abstract

Inputs from deep-sea hydrothermal vents influence ocean geochemical budgets worldwide. Hydrothermal vents produce buoyant and chemically dynamic plumes that are rich in trace seawater elements. The mineral diversity in lower plumes is a direct result of interactions between local geology, hydrology, and biology. Because of this, differences in geochemical trends among naturally occurring plumes are detectable. Past studies have focused on geologic and bulk-chemistry differences between hydrothermal vents (Ferrini et al. 2008; Baker et al. 2005; Pearce et al. 1995; Tivey et al. 2005), while mineral differences among individual plumes remain poorly understood. This study examines and compares lower plume geochemistry of three hydrothermal vents located along the Eastern Lau Spreading Center (ELSC). Deep-sea hydrothermal plumes were sampled by in-situ filtration using ROV Jason2 and the SUPR Sampler (Breier et al. 2009). Samples were collected 0.5 meters above each vent onto polycarbonate membrane filters. Plume particles on the filters were examined by synchrotron radiation X-ray fluorescence (XRF) mapping. Subsequently, a total of 67 filter-bound particles underwent X-ray ray diffraction (XRD) to define the crystalline minerals. Differences among sites are compared and discussed regarding: (1) geologic setting; (2) vent fluid chemistry; and (3) lower-plume mineral species. Reduced metal polysulfides were detected in concentrations that coincide with previous bulk-chemistry studies (Mottl et al., 2011; Tivey et al., 2007; Ishibashi and Urabe, 1995). In addition, this study will introduce a new method to rate confidence levels associated with the identification of mineral species using X-ray microprobe XRD and XRF analysis.