3.5 Ga old terranes in the West African Craton, Mauritania

Evidence for early Archaean relicts in the northern part of the West African Craton are provided from ion-microprobe (SHRIMP) U-Pb zircon and Sm-Nd whole-rock ages in the West Reguibat Rise of Mauritania. The U-Pb ages range between 3515 +/- 15 Ma and 3422 +/- 10 Ma for concordant zircons from an orthogneiss which has also been affected by a 2.7 Ga old metamorphic event, Nd model ages calculated for adjacent metasediments range between 3.9 and 3.5 Ga, suggesting that these supracrustal rocks may be derived from the erosion of a similar early Archaean crust, Zircon ages and Nd depleted-mantle model ages provide the first evidence for an early Archaean crustal growth, at least 3.5-3.6 Ga old, in the West African Craton.