Sub‐surface precipitation of salts in supercritical seawater

Abstract

ABSTRACTExtremely low solubility of typical seawater salts within certain supercritical sections of their pressure–temperature composition space is a proven experimental fact. Its consequences are often referred to as either ‘shock crystallization’ or ‘out‐salting’. Our alternative model for the formation of salt deposits hypothesizes that high temperatures and pressures characteristic for the high heat‐flow zones of tectonically active basins may bring submarine brines into the out‐salting regions and result in the accumulation of geological‐scale salt depositions.To confirm the laboratory observations, molecular‐scale simulations (molecular dynamics) have been employed to study structural changes in a model seawater system where temperature increased from ambient to near‐critical and supercritical. Fluid properties and phase transition regions extracted from the simulations were then used as input parameters for a reservoir simulator program to model out‐salting in a simple hydrothermal geological system. Both numerical simulations and laboratory experiments confirm that supercritical out‐salting is a viable process of geological significance for the formation and accumulation of evaporites. We suggest two regions where hydrothermally associated salts may be depositing today: Atlantis II Deep, in the Red Sea, and Lake Asale, Ethiopia.