Metamorphic and chronological records of early Permian continental collision in Beni Bousera granulites (Internal Rif belt): implications for the tectonic evolution of northern Morocco during Pangea construction

Abstract

This work presents petrologic data obtained from shielded mineral inclusions within large garnets from the Beni-Bousera metamorphic unit (internal Rif belt, northern Morocco) combined with in situ U‒Th‒Pb dating of monazite inclusions. In the considered Beni-Bousera metapelites, the occurrence of mineral inclusions of kyanite + rutile + plagioclase +K-feldspar + quartz ± graphite trapped in garnet cores is diagnostic of high-pressure granulite-facies metamorphism. Geothermobarometry combined with thermodynamic modelling yields minimal P‒T conditions of approximately 1.37-1.5 GPa and 780-795 °C, consistent with the development of palaeogradients during crustal thickening in collision belts. A concordant U/Pb age of 281 ± 3 Ma is obtained from associated monazite inclusions in the same garnet cores. These new petrochronological data attest to the lower Permian continental collision in northern Morocco. The obtained dataset is constrained with petrologic and geochronologic parameters available on other neighboring segments of the Variscan belt. Within the framework of recently unified full plate reconstruction models, the presented tectonic scenario suggests that all these orogenic segments were built during the late Carboniferous-early Permian crustal thickening at the northwestern Gondwana margin in response to the convergence of Laurentia and Gondwana during the late stages of Pangea construction.