The Eovariscan in the Northwest Africa Variscan belt, a key to Paleozoic Africa-Europe connexions: Example of the Mekkam inlier, Morocco

Abstract

The main Variscan phase in Northwest Africa occurred in the late Carboniferous-Permian, which is a late event compared to Western Europe. Yet, an early tectono-metamorphic event is recorded in so-called “Eovariscan” outcrops, mainly in Morocco. In spite of the debate that exists on the tectonic meaning of the Eovariscan event, its P-T conditions and timing are still poorly precised. In only one case are LP-HT conditions recognized and estimated (High Moulouya, Morocco) at 2–4 kbar and 450–650 °C (Filali et al., 1999).The Mekkam inlier (Northeast Morocco) shows Eovariscan deformation affecting Upper Devonian rocks, sealed below unconformable late Visean sedimentary rocks. This deformation overprints inherited metamorphic cordierite and biotite, originally formed during contact metamorphism due to a granodiorite intrusion. The P-T conditions of the deformation have been evaluated through the use of classical metamorphic petrology in addition with Raman Spectroscopy on Carbonaceous Matter for independent temperature estimates. These conditions were then compared to the P-T conditions of emplacement of the granodiorite, determined using the Al-in-amphibole geobarometer (Mutch et al., 2016) and the Holland & Blundy (1994) amphibole-plagioclase geothermometer. P-T conditions for both the granodiorite emplacement and the cordierite-bearing mica schists largely overlap those recorded in the High Moulouya inlier. At last, zircon U-Pb dating on the granodiorite and a late leucogranite have been carried out, whose results are used in order to precise the chronology of events in the Mekkam inlier.The P-T conditions do not support a compressive tectonic context and are more consistent with an extensional one. Our new data confirm the peculiarity of the Eovariscan event in Northwest Africa, which is significantly distinct from the late Carboniferous-Cisuralian Variscan phase. The classical Eovariscan compressional context must be significantly modified because it cannot account for our results and suggest that Northwest Africa behaved in a different manner than Western Europe at the same time. A generalized early Carboniferous rifting context is more suitable to explain our results and data from literature. This could be related to the opening of the Paleotethys, whose influence would be effective as far as northern Morocco and northern Algeria.