THE GREAT AIT KOUZOUD DYKE OF THE ZENAGA INLIER (ANTI-ATLAS, MOROCCO): EVIDENCE FOR PALAEOPROTEROZOIC RIFTING ON THE NORTHERN MARGIN OF THE WEST AFRICAN CRATON

The Neoproterozoic of the Anti Atlas of Morocco is associated with dolerite dikes and sills of the Ifzwana Suite that form a network of intrusions into the Eburnean Zenaga Complex and the lower part of the Taghdout Group. A precise zircon U–Pb age of 2040 +/- 2 Ma was obtained for the Great Aït Kouzoud Dyke - a WNW trending dyke that cross-cuts the Palaeoproterozoic basement of Zenaga Inlier. A similar age of 2040 ± 6 Ma was previously reported for the N-S Ierhourtane dolerite dyke segment which is thought to be part of a WNW trending swarm in the Tagragra of Tata inlier (Walsh et al., 2002). Both dykes are geochemically akin to continental tholeiites. If the inference of a regional WNW-W trend for 2040 Ma dykes in both inliers is correct, then there are two important implications: (i) no significant post-2040 Ma rotation has occurred between the Tagragra of Tata and Zenaga Inliers, and (ii) the projection of the swarm to the northwestern rift margin of the West African Craton may locate a 2040 Ma mantle plume centre, presumably associated with an event of Palaeoproterozoic rifting along the northern margin of the West African Craton. Remarkably, some granites in several inliers of the Anti-Atlas (Zenaga, Tagragra of Tata, among others) are essentially coeval with the 2040 Ma Eburnean (Ifzwane) dykes. This close association in age between the dykes and their host granites suggests that these Eburnian granites could be genetically related to the dolerites (bimodal magmatism). Is it possible that granites were generated by partial melting of lower crust by a 2040 Ma mantle plume?