Origin of Hydrothermal Fluids of the Shallow Submarine Vents of Bahía Concepción, Mexico: An Approach by Geochemical Modeling

We use geochemical modeling to explain the origin of the fluids discharged in the submarine zone of Bahía Concepción, Baja California Sur, Mexico. The geochemical model was performed using REACT program of the computational program Geochemistxs Workbench (release 6.0). The program was executed assuming a polythermal path and a closed system. The selection of the components is based upon fluid inclusions measurements from veins that crop out around the vent discharges. These components are: (a) deep fluid of meteoric origin, (b) high salinity water trapped in the sediments, and (c) seawater. The first mix was between deep fluids with a high salinity fluid. The calculated chemical composition of such fluid fits to a thermal end-member, which mixes with seawater immediately before to be discharged. The fluid obtained by chemical modeling shows calcium, chloride and silica concentrations similar to those of the vent discharges, and salinity and density similar to those calculated from the fluid inclusions study. Geochemical modeling shows that at least three major water components mix in different proportions before the fluid is discharged. Approximately the thermal end-member is composed of 20-30% of the high salinity fluid. The other 70-80% corresponds to a deep fluid that is formed by meteoric water heated by deep penetration. The fluid resultant of the first modeling processes was mixed with seawater and it has a similar chemical composition of the hydrothermal manifestations.