Résumé : Due to different initial Pb incorporation, the PbPb whole-rock data of the Seychelles anorogenic complex of Late Precambrian age form linear arrays (on 24 samples) with no time significance. The existence of two groups of rocks in this complex with different initial Pb and Nd isotopic characteristics has been evidenced: 1. (1) The Mahé group, comprising the biotite-hornblende granite, the weakly alkaline granite and their melanocratic (dioritic to gabbroic) xenoliths, yields ε{lunate}NdBE (705 Ma) = +3.1; their Pb isotopic compositions in K-feldspar are only slightly more radiogenic than those of mantle-derived rocks of the same age. 2. (2) The Praslin-La Digue-Félicité group, comprising the biotite granite and its leucocratic xenoliths, yields ε{lunate}NdBE (705 Ma) = -1.9; K-feldspar Pb ratios are significantly more radiogenic than those of Mahé rocks. Thus, the parental basic magma of this alkaline anorogenic complex appears to originate from a slightly-depleted mantle source underlying the African continental crust. This magma has been contaminated by the high-level part of this crust to different degrees in the two groups, the Praslin one having been more affected, particularly by late-magmatic fluids. © 1984.