• First evidence of eclogite-facies metamorphism in the western Oulad Dlim Massif. • Mafic protolith and host gneisses crystallized during the Ediacaran (584–588 Ma) • Peak P–T of 650–700 °C and 17–19 kbar define a cold subduction gradient (∼10 °C/km) • HP metamorphism dated at 309 ± 3 Ma by SHRIMP U-Th-Pb zircon in eclogite. • Subduction of a stretched continental margin closed the western Paleotethys. The first finding of eclogites in the Lamlaga area of the Oulad Dlim Massif provides new evidence of high-pressure metamorphism in the pericratonic domain of the West African Craton. Petrological, geochemical, and SHRIMP U–Th–Pb zircon age data indicate that these eclogites originated from basaltic protoliths emplaced at 584 ± 6 Ma, coeval with Ediacaran leucocratic intrusions (588 ± 8 Ma). Peak metamorphism occurred at 309 ± 3 Ma at ∼650–700 °C and 1.7–1.9 GPa, as constrained by pseudosection modelling, defining a cold thermal gradient of ∼10–15 °C/km. These P–T estimates are consistent with those reported from other high-pressure units in the Mauritanides Belt, including the Tarf Magneïna eclogites (southern Oulad Dlim Massif, northern Mauritanides) and the Gaouâ Group schists (central Mauritanides), supporting a regional subduction regime during the latest Carboniferous. The metamorphic event is further supported by partially reset U–Pb zircon ages (c. 325–300 Ma) in surrounding Archean to Ediacaran crustal units and Ar–Ar mica and amphibole ages (c. 310–300 Ma) that overprint “Cadomian” ages in the northern and central segments of the Mauritanides Belt to the west of the West African Craton. The spatial and protolith-age coherences between mafic and felsic protoliths, together with the absence of oceanic lithologies, indicate that these eclogites formed through the deep burial of continental rather than oceanic crust. High-pressure metamorphism is interpreted as the consequence of subduction of a thinned passive continental margin following the closure of a narrow oceanic basin, identified here as part of the westernmost Paleo-Tethys realm. This model provides a tectonically and chronologically coherent alternative to traditional interpretations, which link the Mauritanides and the Oulad Dlim Massif to late-Variscan intracontinental deformation associated with the closure of the Rheic Ocean. Our results instead underscore the role of continental subduction in the final amalgamation of Gondwana along its western margin.
Cambeses et al. (Sun,) studied this question.