Lead and bromine enrichment in eclogite-facies fluids: Extreme fractionation during lower-crustal hydration

Hydration reactions associated with eclogite-facies metamorphism of granuli tes in the Norwegian Caledonides led to the formation of saline brines with exceptional compositions. Primary omphacite- and garnet-hosted fluid inclu sions from Norwegian eclogites formed by hydration of granulites contain a plethora of solid phases. A total of 18 different minerals have been identi tied in multiphase brines, and 12 of these occur at the Badsholmen locality in Sunnfjord. Fluid inclusions from this locality are characterized by a h igh Br/CI mass ratio (0.03) and extreme Pb enrichment as demonstrated by th e presence of Pb-bearing daughter minerals including galena, a Pb-CI-bearin g phase, and a Pb-CI-Br-bearing phase. The fluid compositions may reflect e nrichment of elements incompatible with the silicate structure during consu mption of H2O by eclogite-forming hydration reactions. Pb is believed to ha ve been scavenged from the parent granulite by the increasingly saline brin e during K-feldspar breakdown.