The farthest record of the central Atlantic magmatic province into west Africa craton:: Precise 40Ar/39Ar dating and geochemistry of Taoudenni basin intrusives (northern Mali)

The Taoudenni basin dike swarm (northern Mali) is one of the densest dike complexes of the Central Atlantic Magmatic Province (CAMP). A combined geometrical (dike directions), geochemical (major and trace elements, Sr and Nd isotopes), and geochronological (40Ar/39Ar dating) study is presented for the first time on the dikes and sills in this area. The CAMP-related magmatic event is confirmed, revealing a main peak in activity at 198.1 Ma. Dike orientations are clearly correlated with geochemical signatures: the E-W trending dikes have intermediate-Ti concentrations with La/Yb > S; the N-S or NW-SE trending dikes (and the sills) have low-Ti contents, with La/Yb < 7. Although almost all 40Ar/39Ar plateau ages of both dike groups overlap, N-S and intermediate trending dikes could be slightly younger (peak at 197.2 Ma) than the E-W trending dikes (peak at 198.1 Ma). Timing and geochemical evolution on the dikes supported by comparison with contemporaneous lava flows in Morocco suggest that a single sub-continental lithospheric mantle source underwent increasing extents of partial melting (4% during initial stages and 7-15% during later ones) with more pronounced magmatic evolution and crustal contamination in the final stages. Finally, the dike directions are not in agreement with the radial pattern that would be predicted by a plume model for the CAMP. Alternatively, the evolution of the Taoudenni dike pattern may have been controlled by reactivation of older crustal structures and by later massive magma storage at depth in response to thermal incubation beneath the Pangea supercontinent. (c) 2005 Elsevier B.V. All rights reserved.