Physicochemical conditions of hydrothermal processes in the Mid-Atlantic ridge, Fifteen Twenty Fracture Zone

Fluid inclusions were studies in minerals from rocks dredged from the Fifteen Twenty Fracture Zone, Central Atlantic Ocean during Cruise 9 of the R/V Antares (1990-1991). Hydrothermal processes ran at temperatures of 230-250 degrees C (up to 320-405 degrees C) and pressures of about 510-960 bar. The complex multicomponent composition of salt solutions (NaCl-H2O; NaCl-KCl-H2O; NaCl-MgCl2-H2O; NaCl-FeCl2-H2O; NaCl-CaCl2H2O) indicates that both the magma-derived fluids and seawater were involved in the origin of hydrothermal systems. The high salinities of the fluids (8-18 wt % and up to 38-48 wt %) suggest that magma chambers are nearby, which were to a certain extent the sources of the highly concentrated salt solutions.