Contrasting Paleoproterozoic granitoids in the Kerdous, Tagragra d’Akka, Agadir-Melloul and Iguerda inliers (western Anti-Atlas, Morocco)
Résumé
The northern margin of the West African Craton is characterized by Paleoproterozoic siliciclastic sediments intruded by ca. 2.1-2.0 Ga Eburnean granitoids. New geochronological data highlight the occurrence of a Rhyacian (2.10 Ga) tonalitic to trondhjemitic magmatic suite, following a coeval Orosirian (2.040-2.035 Ga) magmatic suite composed of calc-alkaline diorites, mesocratic granites and leucogranites.Whole-rock major and trace element compositions indicate that: (i) the Rhyacian tonalites and trondhjemites suggest a subduction environment, an island-arc arc or an active continental margin; (ii) the Orosirian plutonic rocks show a geochemical heterogeneity; (iii) the chemical features of diorites correspond to calc-alkaline M-type suites; (iv) granodiorites and granites are typical calc-alkaline I-type granitoids, and (iv) leucogranites, with peraluminous composition, reflect a crustal melting.While the Rhyacian magmatic event indicates a subduction environment, the Orosirian magmatic event is more complex, and the geochemical signatures imply involvement of mantellic magmas and crustal melting. The contemporaneity of these Orosirian magmatic suites and their siliciclastic sedimentary host-rocks suggest a back-arc geodynamic context, similar to what was described in the Reguibat Rise, Mauritania.