Abstract

Hydration reactions associated with eclogite-facies metamorphism of granulites in the Norwegian Caledonides led to the formation of saline brines with exceptional compositions. Primary omphacite- and garnet-hosted fluid inclusions from Norwegian eclogites formed by hydration of granulites contain a plethora of solid phases. A total of 18 different minerals have been identified in multiphase brines, and 12 of these occur at the Bådsholmen locality in Sunnfjord. Fluid inclusions from this locality are characterized by a high Br/Cl mass ratio (0.03) and extreme Pb enrichment as demonstrated by the presence of Pb-bearing daughter minerals including galena, a Pb-Cl–bearing phase, and a Pb-Cl-Br–bearing phase. The fluid compositions may reflect enrichment of elements incompatible with the silicate structure during consumption of H2O by eclogite-forming hydration reactions. Pb is believed to have been scavenged from the parent granulite by the increasingly saline brine during K-feldspar breakdown.

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