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Evolution tectono-metamorphique et chronologique des unités métamorphiques du Rif interne (Beni Bousera, Nord du Maroc)

Abstract : Located at the extreme tip of the western Mediterranean, the Betic-Rif orogenic system is built through a complex alpine orogenic history involving processes of subduction related to convergence between Africa and Eurasia since the Cretaceous. A remarkable discovery during the last four decades of geological investigations, has been the remains of a variscan event in the internal zones of the belt. These results underline the presence of two superimposed orogenic systems, the internal zones of the belt thus remain a privileged area to study the importance of the structural and the metamorphic heritage in the partial or total reactivation by the most recent events. This work is located in the Beni Bousera sector, where crustal and mantle rocks that form the innermost units of the chain are exposed. Based on structural and petrological analyses, U-Th-Pb dating on monazite and 40Ar-39Ar dating on micas and amphiboles. The history of the Betic-Rif belt can be summarized as it follows: 1) a HP-HT event affects the base of the internal domain at around 281 ± 3 Ma. These new petrological and geochronological data obtained in the internal Rif, are correlated with the Betics, the Kabyle, the Edough massif of Algeria, the Mauritanian, and the Appalachian belts, attesting a convergent domain during the late Carboniferous – early Permian. All of these orogenic segments are part of the North African Variscides built at the north-western margin of Gondwana in response to convergence between the later and Laurentia. 2) at around 29-26 Ma, a Barrovian to Abukuma metamorphic event affects the Sebtides (the innermost units of the chain) and interpreted as the evolution of the upper plate of a subduction zone. This alpine event is typically characterized by a prograde metamorphic path marked by heating affecting the base of the Sebtides between 26 to 22 Ma, such conditions reflect thinning and heating of the crust related to the asthenosphere upwelling due to slab roll-back. This event marks the beginning of a major extensive event. 3) In the Miocene around 22-20 Ma, the internal zones are affected by an E-W extension contemporary to the opening of the Alboran Basin in a back-arc context, and the intrusion of granitic dykes into the peridotites and crustal metamorphic units, the exhumation of the Sebtides was complete at this time. 4) From early to middle Miocène, the Betic-Rif belt acquired its arcuate geometry (the Gibraltar Arc) during the collision between the Internal and the external zones, attested by de NE-SW to E-W shortening phases across the arc. 5) more lately prior to Pliocene, the Gibraltar arc was subjected to contractional possess related to a N-S shortening phase, which drastically altered its geometry.
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Submitted on : Tuesday, September 14, 2021 - 11:49:12 AM
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Asmae El Bakili. Evolution tectono-metamorphique et chronologique des unités métamorphiques du Rif interne (Beni Bousera, Nord du Maroc). Sciences de la Terre. Université Côte d'Azur; Université Mohammed V (Rabat). Faculté des sciences, 2021. Français. ⟨NNT : 2021COAZ4034⟩. ⟨tel-03343636⟩

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