Carmenchu Peak forms a solitary volcano on the central Atlantic Ocean upper continental rise off West Africa. Extrusives dredged from the central and upper slopes of the seamount formed during alkalic capping phase flank eruptions, and range in composition from picritic basalt to trachyte. K-Ar age determinations reveal that the entire alkalic sequence formed over a relatively short time interval of 6 Ma during the Cenomanian. The submarine volcanic edifice is likely a hot spot flare product. Pb, Sr and Nd isotope signatures identify isotopically mantle reequilibrated ancient recycled subducted lithosphere (HIMU) as main source component of alkalic rocks. Model calculations reveal that <1% of pelagic sediment or sediment-derived fluids were incorporated in the OIB source generating the alkali portion of the seamount.