Water-rock interaction in hydrothermal systems at 'liquid-vapor' equilibrium conditions: An experimental approach

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Given the fact that many sections of slow-spreading ridges are at water depths greater than 3000 m, the submarine hydrothermalism at 5°S on the Mid Atlantic Ridge (MAR) with extreme fluxes of heat, metals and unique rare earth element chemistry (REE) is of general significance for oceanic element budgets. Transport-reaction processes in these high-pressure (p) / high-temperature (T) hydrothermal systems are poorly constrained. We propose (1) experiments under p-T-conditions similar to those at MAR 5°S for the study of seawater-rock interaction and resulting element partitioning as well as (2) of time-resolved rock alteration and generation of secondary minerals and (3) subsequent modelling of time-integrated changes of fluid and rock chemistry. The starting materials will be natural Atlantic Deep Water reacting with unaltered gabbroic fragments from IODP Hole U1309D (gabbro: 1020 m bsl, Olivine-gabbro: ~1050 m bsl, troctolite: ~1125 m bsl; only experiments with gabbro were performed in the first period of funding). In addition, a systematic study of elemental composition and REE pattern of secondary mineral assemblages of recovered basaltic and gabbroic samples from IODP Site U1309D will - together with other data from the literature - help to better interpret our experimental findings and understand the natural alteration processes of oceanic crust. In summary, our experimentally derived water-rock partitioning behaviour of transition metals and REE as well as the modelling will add to our knowledge of seawater-rock interaction processes and will improve our understanding of transport reactions and element fluxes during ascent in hydrothermal systems that run at extreme temperatures and great water depths.