U–Pb geochronology of Variscan granitoids from the Moroccan Meseta (Northwest Africa): Tectonic implications

Abstract

This paper present new U–Pb geochronological data (LA-ICP MS on zircon) of granitoids from the Moroccan Meseta Variscan belt. Zircons from the Oulad Ouaslam granodiorite in the Jebilet massif in the Western Meseta highlight a peak of magmatic activity at 335.2 ± 0.8 Ma. In the Eastern Meseta, the ages obtained from several granitoids facies from the High Moulouya magmatic complex restrained its magmatic activity to the early Visean: 339.6 ± 1.9 Ma for the Perdreaux granite, 337 ± 1.6 Ma for the calc-alkaline «grey» granite and 343.1 ± 1.2 Ma for the El Hassir granodiorite. Similar late Tournaisian – early Visean ages were obtained for the Zekarra granodiorite (348.1 ± 2.3 Ma) and the Merguechoum granite (345.2 ± 2.8 Ma) in the Horsts belt. This pre-orogenic Eovariscan magmatic activity is contemporaneous with the opening of early Carboniferous intracontinental basins in the whole Northwest Africa but its relationship with Eovariscan deformation typifying the Eastern Meseta remains temporally unclear. Then, the late Carboniferous ages of 308.2 ± 2.7 Ma obtained for the Beni Snassen monzogranite, 303.5 ± 1.7 for the Tanncherfi granodiorite and 305.2 ± 1.4 for the Boudoufoud granite in the Horsts belt show that they all are synchronous with the main late Carboniferous convergent Variscan event in Northwest Africa. This tectonic and magmatic tempos contrast with the one described in the European Variscan belt, where the syn-collisional magmatism forms coevally with the Northwest African Eovariscan event, re-interpreted as a possible extensional event. We proposed that the early Carboniferous intracontinental basins and magmatism in Northwest Africa are due to the propagation of the Paleotethys ocean within the Gondwana continent. In contrary, the late Carboniferous – early Permian tectono-magmatic activity could reflect the docking of the east Gondwana margin with the Iberian branch of the European Variscan belt.