Mixing vs Boiling process in a shallow submarine hydrothermal system of Bahía Concepción, Mexico

In this paper we use geochemical modeling and fluid inclusions to support the hypothesis that the main process that undergoes the fluid discharged by submarine vents in Bahia Concepcion is mixing rather than boiling. Mixing modeling of two different fluids: a high salinity fluid that is mixed with a deep thermal fluid of meteoric origin indicate that the thermal water responsible for the formation of the thermal EM of Bahía Concepción is composed by 20-30% of a HDF and 70-80% of a hot DF of meteoric origin. Boiling would be an alternate process; however, fluid inclusions petrography and microthermometry reveal no boiling evidence present in the samples, as breccias, bladed calcite, or coexisting liquid-rich and vapor-rich inclusions. Furthermore, the salinity of pseudosecondary and secondary fluid inclusions is similar to seawater. The mixing model is consistent with fluid inclusion data, which provide evidence that two different hydrothermal fluids are involved in barite deposition at veins related to the submarine manifestations of Bahía Concepción: a low salinity fluid (139°C and 3.2 wt % NaCl eq) and HSF (129°C and 10.6 wt % NaCl eq.) The trend observed between high- to low-salinity fluids shows the occurrence of mixing processes between both hydrothermal fluids.