High‐Pressure Granulite Facies Metamorphism in the Pan‐African Dahomeyide Orogen, West Africa

Abstract

High‐pressure (HP) granulite facies rocks are associated with eclogites in the Pan‐African Dahomeyide orogen, West Africa. The HP‐granulite and eclogite facies mineral assemblages occur in mafic gneisses within the suture zone exposed in southeastern Ghana and the adjoining part of Togo. Thermobarometric calculations and phase equilibria considerations indicate that the HP metamorphic rocks preserve a record of: (i) prograde garnet crystallization during eclogite facies metamorphism as temperature increased to a maximum of ∼600°C and pressure reached >18 kbar, followed by (ii) HP‐granulite facies metamorphism when temperatures reached 800–900°C at P ∼14 kbar, resulting in partial melting to produce leucocratic veins. Decompression along a retrograde path is inferred from granulites that yield temperatures down to ∼700°C at ∼10 kbar. The inferred P‐T path of the metamorphic record defines a clockwise loop in the kyanite stability field, compatible with orogeny involving subduction during the Pan‐African as...