BERYLLIUM ISOTOPE SYSTEMATICS OF SUBMARINE HYDROTHERMAL SYSTEMS

Both Be-10 and Be-9 concentrations have been measured in a hydrothermal fluid from the sediment-starved East Pacific Rise at 21-degrees-N as well as in fluids and associated sediments from the sediment covered Guaymas Basin and Escanaba Trough hydrothermal systems. The results show that while the Be-9 concentrations in fluids from both types of systems are comparable, about three orders of magnitude higher than that of the seawater supplying the systems, their Be-10 concentrations are significantly different. The Be-10 concentration in the solution emanating from the studied sediment-starved hydrothermal system is at least two times lower than that of the Pacific bottom water. By contrast, the Be-10 concentration in hydrothermal solutions from sediment-hosted environments are enriched over ambient seawater and are at least one order of magnitude higher than that measured in the 21-degrees-N fluid. The sedimentary cover being the only available source of Be-10 in these systems, these data demonstrate that Be-10 is an unambiguous tracer of interactions between hydrothermal fluids and recent sediments. As an example, this study examines hydrothermal solutions from the sediment-starved Mariana Trough back-arc basin which have compositions similar in many respects to those from sediment-hosted environments. However, these fluids are depleted in Be-10 relative to ambient seawater, which precludes interaction with recent sediment as the cause of their peculiar chemical composition.