The coexistence of arc- and enriched-mantle-related mafic suites within the Winneba Segment: Implications for the geodynamic evolution of the Rhyacian Birimian Terrane of West Africa

Both arc-related and enriched-mantle rocks occur within the Paleoproterozoic Birimian terrane; however, the geological implications of this remain enigmatic. This study thus investigates the geological implications of this occurrence by integrating major and trace element data from the mafic suites of the Winneba Segment and published geochemical data from other Birimian belts in Ghana. The Winneba Segment mafic suites are dominantly subalkaline basalts, with minor basaltic andesite and andesite similar to the other Birimian belts. Geochemical features of the Winneba Segment mafic suites and the other belts characterised by negative Nb-Ta peaks, enriched large-ion lithophile element, light rare earth element, and depleted high-field strength element support formation in an arc setting through subduction–accretionary processes. They are characterised by La/Nb of 0.9–7.2, Ti/Zr of 24–154, moderate to high Nb/Yb, and high Th/Yb values. The low values are characteristic of arc-influenced magmas, whereas the spread to very high ratios might indicate magma–crust interaction during their evolution. A few mafic suites of the Winneba Segment and the Bui Belt exhibit an enriched-mantle character with positive Ta, Nb, and Ti anomalies. The new geochemical data for the mafic suites of the Winneba Segment, and previously published data from mafic suites in other Birimian belts in Ghana, reveal the presence of two distinct types of mafic suites: enriched- and arc-related. The arc-related mafic suites are proposed to be associated with subduction-related accretionary processes during the Rhyacian Eburnean orogeny, while the enriched-mantle signature may result from magma–crust interaction and possibly sediment/upper-crustal contamination.