Numerical Modeling of Supercritical Out-Salting in the Atlantis II Deep (Red Sea) Hydrothermal System

Supercritical water behaves close to that of a non-polar fluid and its ability to dissolve salt ions is very low. In rifting locations world-wide, where hot vents occur, it has been shown that seawater attains supercritical conditions. We therefore anticipate that circulation of seawater in hydrothermal systems passing through regions of the supercritical domain results in spontaneous precipitation of salt particles. Thus, the hot ‘geysers’ of saturated brines observed in the ‘Atlantis II Deep’ of the Red Sea could result from re-dissolution of salts accumulated in underground fracture systems. Here we report on an advanced numerical modeling study which demonstrates, for the first time, that there is a forced convection cell where salts precipitate and accumulate. These combined numerical thermodynamic simulations and basin modelling results also demonstrate that hot brines reflux back to surface immediately above the magma chamber located beneath the axis of the rift. Based on this study, we predict that hydrothermal ‘out-salting’ is the main cause of dense, warm brines accumulating in the central portion of the Red Sea. Furthermore, the results are relevant for understanding how large volumes of evaporites (salts) accumulate along rifted plate margins.