ABSTRACT
At the bottom of the terrestrial oceans, where tectonic forces separate the lithospheric plates along mid-ocean ridges, the ultramac rocks of the upper-mantle, the peridotites, are exposed to circulating seawater [1]. ey encounter various physico-chemical conditions and the hydrolysis of their silicate constituents, the olivine and pyroxenes minerals, into serpentine, occur at dierent degrees of serpentinization depending on the characteristics of the medium: temperature, pressure, oxygen fugacity, nature and composition of the uid phase, uid ux, pH, rock composition, water:rock ratio [2]. e Mid-Atlantic-Ridge, MAR, is covered with several hydrothermal sites and presents black smoker activity. e active Logatchev site, 14° 45’N-43’N, at a water depth of 2,970 m and the active Ashadze site (12° 58’N, 4,080 m) are located on an ultramac geological environment of serpentinized peridotite rocks, while the Krasnov site (16° 38’N), discovered with the Ashadze site during the 2007 French-Russian Serpentine cruise [3] is inactive and located on a basaltic environment. Ultramac environments seem enriched in Cu and Zn content compared to the basaltic ones [3].
