Large molybdenum isotope variations trace subsurface fluid migration along the Dead Sea transform

Large (-0.6 parts per thousand to +2.3 parts per thousand) delta(97/95)Mo variations occur in molybdenum-enriched iron oxide veins located in anticlines adjacent to the Dead Sea transform, and are thought to reflect the solutions from which the veins formed because of efficient scavenging of Mo by iron oxides. The wide range of delta(97/95)Mo values occurs in a paleohydrologic setting in which dense, concentrated, evaporitic marine brines in the Dead Sea Rift valley (delta(97/95)Mo similar to 1.6 parts per thousand) penetrated and interacted with sedimentary rocks of the rift flanks, which included Cretaceous bituminous chalks (delta(97/95)Mo 0.8 parts per thousand-1.2 parts per thousand), before intermixing with Fe-bearing groundwater containing molybdenum of igneous and clastic origin. The delta(97/95)Mo values higher than seawater (1.6 parts per thousand-2.3 parts per thousand) are attributed to Rayleigh isotopic fractionation along the path of the brine migration. Molybdenum isotopes thus reveal a powerful potential to trace the sources and processes governing subsurface metalliferous fluid migration.