Petrogenesis and geochemistry of WNW-ESE to NW-SE trending doleritic dykes of the Paleoproterozoic Liptako basement (West African Craton, West Niger)

Doleritic dykes with regional orientations WNW-ESE to NW-SE, cut the Paleoproterozoic Birimian formations of the Liptako basement (Ouest-Niger). Mineralogical compositions studied from these doleritic dykes consist of augite (Wo21-40-En24-45-Fs13-54), pigeonite (Wo8-12-En45-59-Fs31-41), plagioclase, alkali feldspars, titano-magnetite, ilmenite, edenite, apatite, biotite and chlorite. The geochemical affinity of the doleritic dykes in the two trends is similar to oceanic plateau basalts (OPB), with high iron content relative to Mg. Negative Nb, Ti and Ta anomalies and the Y/Nb ratio (1.59–3.15) indicate a continental tholeiitic character for while light rare earth element enrichment, low to moderate Ti contents and the Th/Yb (0.28–0.59) and Nb/Yb (3.25–7.46) ratios suggest sources similar to E-MORB. Their Th/Nb (0.06–0.10), Th/Yb (0.28–0.59), TiO2/Yb (0.54–0.82) ratios suggest that the magma was generated by partial melting (5–17%) of a residual spinel-garnet lherzolite, that could have been part of a mantle plume. Relatively low Mg# (36–51) reflect some degrees of fractional crystallization, with some of this differentiation recorded between the margins and interiors of dykes. This differentiation was accompanied by unusually low degrees of crustal contamination, as indicated by relatively low Th/Ta ratios (1.18–2.03). This petrological and geochemical information provides n.ew constraints on the origin of these WNW to NE trending mafic dykes of the West African Craton. •Mineralogical composition of the dykes determined by electron microprobe.•Spatial distribution of chemical elements on the crystals revealed by chemical mapping.•Similar affinity to oceanic plateau basalts and E-MORB suggested by whole rock analyses.•Garnet-spinel lherzolite source and an intraplate setting indicated by geotectonic diagrams.