Petrogenesis, geochemistry and structural evidence of the neoproterozoic Pan-African orogenic event in Ghana, West Africa

Abstract

Certain parts of Ghana (Eastern and Volta region) are predominantly covered by neoproterozoic Dahomeyide rocks which occurred during the Pan-African Orogeny event in West Africa. To understand the petrological, geochemical and structural evidence of this geologic event, a detailed geological mapping exercise was conducted in some parts of the Eastern and Volta regions of Ghana. The aim of this research is to understand the local geology of these areas and how it best fits the regional geology of Ghana and its implications in the Pan-African Orogenic event. The evidences presented in this study show that the rocks in these areas are mainly metamorphic, which are granitic augen gneiss, biotite gneiss and quartzite. The gneisses were proposed to belong to the basement Dahomeyan, while the quartzites belong to the Togo Structural Unit. It was also inferred that the rocks have been deformed mainly by brittle and ductile deformation, resulting in structures such as foliations, fractures and joints observed in the quartzites and gneisses within the area of study. The structures within the study area have a general attitude of north-east–south-west with some few structures trending in the north-west–south-east directions. Again, it was inferred that the rocks from the Dahomeyan structural unit are highly metamorphosed and deformed as compared to the rocks from the Togo structural unit. The granitic augen gneiss and biotite gneiss have rock-forming minerals such as biotite, K-feldspar, quartz, muscovite, plagioclase and hornblende in varying proportions, whereas the quartzites are predominantly composed of glassy quartz crystals.