Zircon Hf and O-isotope constraints on the evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton

The use of zircon isotopic systems, such as Lu-Hf and O, has proven to be an invaluable tool for unraveling the evolution of the early Earth. In order to achieve a comprehensive understanding of the evolution of the southern West African Craton and, in particular, the Paleoproterozoic Baoulé-Mossi domain, zircon grains from 75 felsic intrusions were analyzed for Hf-isotopes; 22 of those samples were analyzed for O-isotopes covering an area that covers more than 1000 km2, from southwest Burkina Faso across southern Mali and into eastern Guinea. The results of the study reveal that the Baoulé-Mossi domain comprises two magmatic regions that display broadly juvenile isotopic character, but with significant localized evidence of crustal contamination. The Hf model age data show that the crustal contaminant is potentially as old as ca. 2800 Ma and indicate that the two domains may have evolved slightly differently. In fact, the westernmost region presents a slightly older (or less radiogenic) Hf-isotope signature when compared to the easternmost region. Furthermore, the O isotopic data support the notion that the felsic magmas were subject to supra-crustal contamination, as δ18O values range between 6 and 12‰. The data presented in this study provide robust evidence that the Baoulé-Mossi domain of the southern West African Craton evolved by accretionary processes between ca. 2250-2050 Ma.