Red Sea Salt Formations—A Result of Hydrothermal Processes

A new conceptual model, called 'the hydrothermal salt model', predicts that salt may accumulate in the marine sub-surface from the hydrothermal circulation of sea water. The hypothesis is based on the physicochemical behaviour of supercritical sea water; when sea water is driven into its supercritical high-temperature and high-pressure domain (407 degrees C, 298 bars), it loses its solubility for the common sea salts (chlorides and sulphates). Consequently, a spontaneous precipitation of salts takes place in the water-filled pore spaces. The same process may occur when porous rocks containing saline pore water are exposed to sufficiently high temperature and pressure, for example in the subduction of oceanic crust. Salts will also precipitate sub-surface or sub-marine during boiling, in contact with high heat flow sources, such as magma intrusions. Large accumulations of salt are found within the central trough and along both sides of the Red Sea rift. Many of the associated accumulation features are difficult to explain in terms of the conventional 'evaporite' model for salt deposits. The features are as follows: (1) several kilometre thick salt deposits on both flanks of the Red Sea, (2) thick (similar to 3 km) salt deposits inside the central graben, (3) dense, hot brines inside some of the central graben deeps (Atlantis II Deep, Conrad Deep, etc.), (4) up to 40-km-long walls and ridges of exposed salt on the northern Red Sea seafloor, (5) tall walls of salt adjacent to the Conrad Deep central graben, and (6) large flows of salt in the Thetis Deep. Furthermore, these huge accumulations of salt took place in a relatively short geological period of time. On the basis of these pertinent structures and features, it is concluded that accumulation, deformation, and transportation of salts may have several drivers and origins, including a process closely associated with hydrothermal activity. Whereas hydrothermally produced salts are lost directly to sea water in mid-ocean spreading hydrothermal systems, they are protected by sediments and ponded high-density brines on the seafloor in deep-spreading centres like that of the Red Sea. Because the Red Sea is the closest active analogue to the rifting and rupturing of 'Atlantic-type' continental lithosphere, it may also be the key to understanding the accumulations of huge underground salt deposits and salt-related structures in some of the world's ancient deep-water rifted margins.