FY 1999

Helium, heat, and the generation of hydrothermal event plumes at mid-ocean ridges

Lupton, J.E., E.T. Baker, and G.J. Massoth

Earth Planet. Sci. Lett., 171(3), 343–350, doi: 10.1016/S0012-821X(99)00149-1 (1999)

Hydrothermal event plumes are unique water-column features observed over mid-ocean ridges, presumably generated by the sudden release of large volumes of hot, buoyant fluid. Although the specifics of event plume generation are unknown, event plumes have been attributed to the rapid emptying of a hydrothermal reservoir or to rapid heat extraction from a recently emplaced dike or seafloor lava flows. The chemical and thermal signatures of event plumes as compared to the underlying steady-state plumes offer important clues to the generation of event plumes. Event plumes have low ³He/heat ratios of ~0.4 × 10^–17 mol J^–1, similar to vent fluids from mature hydrothermal systems. In contrast, the steady-state plumes found beneath the event plumes have elevated and variable ³He/heat ratios of 2 to 5 × 10^–17 mol J^–1, up to 30 times the event plume values. These disparate³He/heat ratios place strong constraints on models of event plume generation, especially models which rely on heat extraction from seafloor eruptions.