Neoproterozoic granitoids in the basement of the Moroccan Central Meseta: Correlation with the Anti-Atlas at the NW paleo-margin of Gondwana
Résumé
Field observations and U–Pb LA–ICP–MS zircon ages of magmatic outcrops in the Goaïda area, south-eastern part of Moroccan Central Massif (Meseta domain), provide firm evidence of Neoproterozoic silicic magmatism in the basement of the Moroccan Variscan belt. This magmatic activity produced three distinct plutons —dark, pink and white granitoids—, which form a Neoproterozoic basement strongly reworked in the Carboniferous and intruded by Hercynian gabbro, dolerite and rhyolite bodies. The Goaïda dark granitoids are syeno–granodiorites, whereas the pink and white granitoids are granites sensu stricto. All the facies of Goaïda granitoids have I-type, high-K and calc-alkaline affinities. Concordant U–Pb zircon data yield Lowermost Ediacaran mean age for white granites (625 ± 9 Ma) and Ediacaran mean ages for dark granitoids (600 ± 10 Ma) and pink granites (552 ± 10 Ma). White granites record old high-K calc-alkaline magmatism that started in the Anti-Atlas belt at ca. 620 Ma, coinciding with the end of the second period of the Pan-African orogenesis. On the other hand, the dark and pink granitoids formed in subduction-related to post-collisional regimes during the final stage of the Pan-African orogenesis, namely the WACadomian orogeny. We combine new field, geochronological and geochemical data with results from the literature to propose a new lithostratigraphic reconstruction of the Precambrian to Early Cambrian times in the Moroccan Meseta front at the NW margin of the West African Craton. The presence of Precambrian outcrops —including Paleoproterozoic and Neoproterozoic rocks— in the Moroccan Variscan belt demonstrates the continuity of the peri-Gondwanan Panafrican basement at least from the eastern Anti-Atlas to the Central Meseta domain. Along with the lack of Paleozoic ophiolitic suture and subduction-related metamorphic rocks, this continuity supports the hypothesis that the Moroccan Variscan mountains were part of the NW margin of Gondwana in the Paleozoic.