PRELIMINARY RESULTS OF A FLUID INCLUSION STUDY ON UPPER CRETACEOUS JUDEA GROUP DOLOMITES IN THE DEAD SEA REGION, ISRAEL

The region west of the Dead Sea rift in Israel contains several hundred meters of Upper Cretaceous carbonate rocks. Dolomitization of these rocks is complete or near complete close to the Dead Sea, but little or no dolomite is present in the rocks to the west. These rocks were never buried by more than 300 to 400 m of sediments. Preliminary data from a fluid-inclusion study of calcite, dolomite, and barite suggest that a local hydrothermal system was responsible for some of the calcite and dolomite mineralization in the region. Coarse planar and saddle dolomite is prevalent in the Nezer and Shivta Formations and is found as tabular and finger-shaped masses near joint and fault intersections. These dolomite bodies are interpreted as the upper reaches of the flow system that carried dolomitizing fluids. Both all-liquid and two-phase aqueous fluid inclusions are found in different fluid inclusion assemblages in dolomite, calcite, and barite from the region. Homogenization temperature data from primary fluid inclusions in two dolomite samples suggest that the bulk of dolomitization occurred at temperatures of at least 55 to 70°C, and some data indicate that higher temperatures (~80 to 100°C) may have existed. Only secondary fluid inclusion assemblages (FIA) with mostly all-liquid inclusions were observed for barite. In massive calcite from near a fault zone at Massada, both all-liquid and two-phase aqueous secondary FIA were observed. The two-phase inclusions were very consistent and indicate that temperatures of at least 55°C were present. Nearly all inclusions measured in the three minerals had final melting temperatures of ice that ranged between -4.0 and 0.0°C. One inclusion in dolomite had a final melting temperature of -9.7°C. The salinity of the dolomitizing fluids was significantly lower than that of the Dead Sea brine. Several conceptual fluid flow models are possible. One model involves westward and upward moving fluids that penetrate the Upper Cretaceous carbonate section. Both density and topography-driven models are possible, and these are currently being evaluated.