Thermal anomalies associated with forced and free ground-water convection in the Dead Sea rift valley: Discussion and reply

Abstract

modeling as a basic tool for understanding hydrogeologic and hydrothermal systems in the Dead Sea rift valley in the Sea of Galilee region. They say that,“The existence of free convection cells of deep ground water...which has never been suggested previously, is hypothesized on the basis of...modeling” (Gvirtzman et al., 1997, p. 1175). They demonstrated that geothermal anomalies result from ground-water convection systems, which distribute the heat. They believe that through their study they have gained insights into the processes that create hot springs. Gvirtzman et al. (1997) presented a most convincing argument. In their paper they refer to an alternative interpretation for a regional heat anomaly attributed to the extensive Miocene–mid-Pleistocene volcanism and intrusions (Arad and Bein, 1986). They feel that this explanation may be less relevant because the heat anomaly is observed only locally, and any intrusions probably have cooled since the last eruption took place 0.7 Ma (Mor and Steinitz, 1984). In my study of the sediment in this same area, I have used a different approach that seems to support the influence of volcanism and that supplements and complements the data of Gvirtzman et al. (Friedman, 1995). My interest was the origin of dolomite in the sediment of the Tiberias Hot Springs along the shores of the Sea of Galilee (Friedman, 1995). The Sea of Galilee region is located within the Dead Sea transform, which joins the Red Sea transform via the Gulf of Aqaba. These plate boundaries host hydrothermal exhalations that raise the question of fluid processes at these boundaries. As an example, the circulation of seawater through the still-hot oceanic crust within the Red Sea axial zone has produced hot brine pools (Degens and Ross, 1969; Backer and Schoell, 1972; Amann et al., 1973; Backer, 1975; Coleman, 1993). In the Red Sea, at least 18 hot brine pools have been discovered and new ones continue to be reported as more detailed oceanic studies are carried out. The composition of the brine has been compared with hydrothermal fluids emanating from active “black smokers” of the East Pacific Rise and Juan de Fuca Ridge. The similarity of these fluids is striking in that they are all saturated with NaCl and are enriched in Na, K, Rb, and Ca when compared to seawater (Coleman, 1993). These brines are thought to have been derived from deep circulation of hydrothermal fluids within the underlying basalts at high temperature. Along the Dead Sea strike-slip basin, brines form carbonate and evaporite