Geochemical Constraints Provided by the Freetown Layered Complex (Sierra Leone) on the Origin of High-Ti Tholeiitic CAMP Magmas

The Freetown Layered Complex (FLC) is a massive mafic layered intrusion cropping out along the coast of Sierra Leone. The present combined geochemical and geochronological (40Ar/39Ar on plagioclase: 201·7 ± 0·7 and 202·3 ± 2·3 Ma; U–Pb on baddeleyite: 198·794 ± 0·048/0·071/0·22 Ma) study of the complex flags it as a high-Ti occurrence of the Central Atlantic Magmatic Province (CAMP). Sr–Nd–Pb–Os isotope data indicate that the FLC is unique with respect to previously studied CAMP occurrences, constituting a new isotopic end-member for this large igneous province (LIP). Notably, the contribution of ancient source(s) is required to explain its low 206Pb/204Pb and high 207Pb/204Pb. Although the internal isotopic variability of the FLC can be explained by modest assimilation (