Stable Isotopes in Seafloor Hydrothermal Systems: Vent fluids, hydrothermal deposits, hydrothermal alteration, and microbial processes

Abstract

The recognition of abundant and widespread hydrothermal activity and associated unique life-forms on the ocean floor is one of the great scientific discoveries of the latter half of the twentieth century. Studies of seafloor hydrothermal processes have led to revolutions in understanding fluid convection and the cooling of the ocean crust, the chemical and isotopic mass balance of the oceans, the origin of stratiform and statabound massive-sulfide ore-deposits, the origin of greenstones and serpentinites, and the potential importance of the subseafloor biosphere. Stable isotope geochemistry has been a critical and definitive tool from the very beginning of the modern era of seafloor exploration. Early suggestions of possible submarine hydrothermal activity date from the late 1950s when a number of investigators were debating the importance of “volcanic emanations” as a factor in the widespread occurrence of manganese nodules and other ferromanganese oxide deposits on the seafloor. Arrhenius and Bonatti (1965), in their classic paper, Vulcanism and Neptunism in the Oceans, stated the following: “The origin of authigenic minerals on the ocean floor has been extensively discussed in the past with emphasis on two major processes; precipitation from solutions originating from submarine eruptions, and slow precipitation from sea water of dissolved elements, originating from weathering of continental rocks. It is concluded that in several marine authigenic mineral systems these processes overlap.” Bostrom and Peterson (1966), in another classic, published evidence for extensive and widespread Fe-rich metalliferous sediments on the seafloor with a distribution strongly correlated with the mid-ocean ridges (Fig. 1⇓). They stated: Figure 1. Distribution of metalliferous surficial sediments, enriched in (Al+Fe+Mn)/Al, around divergent plate margin (modified after Bostrom et al. 1969). Used with permission of the American Geophysical Union. “On the very crest of the East Pacific Rise, in equatorial latitudes--particularly 12° to 16°S, the sediments are enriched in …