Petrographic and Geochemical Characteristics of the Akaba Igneous Massif from the Pan-African Orogen in Togo, West Africa

Abstract

The Dahomeyide orogen in Togo and adjoining parts of southeast-Ghana and Benin represents the West Africa Craton (WAC) suture into northwest Gondwana. The suture zone is a narrow and lithologically diverse region with high pressure granulites complexes. The Akaba massif located in the central part of Togo, belongs to this suture zone. Petrographical and whole rock geochemical analyses are used to evaluate the characteristics, petrogenesis and mode of emplacement of the Akaba massif. The new data suggest that the Akaba massif is built by layered amphibolites, garnet-free granulites and metapyroxenites. These rocks were equilibrated under granulite facies conditions and subsequently partially retrogressed to the amphibolite facies. Geochemical suggest that the granulites may have preserved the geochemical imprints of their igneous protoliths. They display tholeiitic affinity, slightly enriched LREE, no Eu anomaly and negative anomalies in Nb and Zr indicate subduction zone magmatism. These features are consistent with protoliths of N-MORB affinities. The Akaba massif rocks were emplaced up in an oceanic arc environment and likely originated from a metasomatized mantle.