OS43A-2024
Thermo-chemical fluxes, reactions and mixing in hydrothermal plumes at Oceanic Core complexes (Mid-Atlantic Ridge, 13°30’N and 13°20’N)

Thursday, 17 December 2015
Poster Hall (Moscone South)
Christine Destrigneville1, Valérie Chavagnac1, Jean-Arthur L Olive2, Thomas Leleu1, Céline Rommevaux3, Javier Escartin4, John W Jamieson5 and Sven Petersen5, (1)GET Géosciences Environnement Toulouse, Toulouse, France, (2)WHOI, Woods Hole, MA, United States, (3)Institut de Physique du Globe de Paris, Paris, France, (4)CNRS, Paris Cedex 16, France, (5)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
Abstract:
Large-offset detachment faults are widespread along the slow-spreading Mid-Atlantic Ridge (MAR), exhume ultramafic rocks, and host a great diversity of hydrothermal systems. During the ODEMAR’13 cruise, the fully developed 13º20’N and 13º30’N oceanic core complexes (OCC) along MAR were investigated to constrain the tectonic, hydrothermal and magmatic processes enabling detachment formation. Here we focus on the composition and fluxes of hydrothermal fluids discharging out of these OCCs.

 ROV Victor6000 dives confirmed the occurrence of active discharge near the breakaway side of the 13º30’N OCC (Semenov-2), and observed high-temperature venting on the striated fault surface of the 13º20’N OCC (Irinovskoe). Black smoker fluids and hydrothermal plume waters (2-110ºC) were collected using gas-tight titanium syringes and in-situ pumping fluid samplers mounted on the ROV, respectively. The Semenov-2 fluids (3 vent sites at 317ºC) are characterized by lower chlorinity than seawater (Cl = 525 mmol/l) and extremely low metal concentrations (Fe, Mn, Cu, Zn < ~20 μmol/l). By contrast, the Irinovskoe fluids (2 vent sites at 364ºC) exhibit higher chlorinity than seawater at Cl = 605 mmol/l, high Fe and Mn concentrations, and yet low metal concentrations.

Temperature and concentration of conservative species were also measured along the centerlines of selected plumes within the first ~3 m above the vents. These measurements were inverted to constrain vent heat and mass fluxes using a plume entrainment model, yielding for individual plumes values of ~1-95 MW and 1-60 10-3 m3/s, respectively. We use these to calculate annual filterable iron fluxes at both sites of the 13º20’N OCC of 2.6 – 3.9 106 mol/yr, which are 4 orders of magnitude higher than those calculated for the 13º30’N OCC. We estimate, however, that ~94% of this Fe flux is lost through precipitation when rising hydrothermal fluids mix with entrained seawater.

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