Tectonics of the North African Variscides (Morocco, western Algeria): an outline

Abstract

The Palaeozoic terranes that crop out north of the South Atlasic Line constitute the Variscan Belt of North Africa. Subdivision of the belt into five structural zones separated by major shear zones results from a polyphase evolution including very localised Prevariscan events (450-430 Ma), which correspond to the Caledonian cycle, and Variscan events involving three main stages: Eovariscan (370-360 Ma), Mesovariscan (330-320 Ma), and Neovariscan (300-290 Ma), followed by Tardi-Variscan events during Early Permian-Triassic times. During the Variscan evolution, the geodynamic context is transtensive-transpressive, and controls the opening and closure of Devono-Carboniferous basins. The Variscan deformations are accommodated by folding and combination of thrusting and strike-slip faulting associated with a low-grade to medium-grade metamorphic evolution, characteristic of the external zones of the orogens. The lack of oceanic crust, and thus of suture zone in the Palaeozoic series suggests that the North African Variscan Belt is an intracontinental part of the Variscan orogen, which evolved near the margin of the West African Craton. The links with the other Periatlantic Palaeozoic segments still remain a subject of discussion.

Inversion tectonics, interference pattern and extensional fault-related folding in the Eastern Anti-Atlas, Morocco

“…2). The Anti-Atlas possibly corresponds to a Paleozoic foreland fold-belt, which can be regarded as the deformed foreland of the Variscan chain present in Morocco in the "Moroccan Meseta" (Hoepffner et al 2006;Raddi et al 2007) (Fig. 1).…”

Tectonics of the Anti-Atlas of Morocco

“…It is thus quite obvious that the Moroccan Meseta underwent a very different tectonic history as compared to that of the Anti-Atlas, from the Ordovician onward [69,71]. Many parts of the complex assemblage of units in the Meseta have suffered several intense phases of deformation, metamorphism including the intrusion of granites in Silurian times and from the Lower Carboniferous onward [49]. In this respect, the Meseta is comparable to the internal Appalachian chain, with its Taconic and Acadian belts.…”

“…Such fragments would have been accreted again to the African craton only during the latest stages of continent-continent collision in Late Carboniferous [14,33]. Such mobilistic proposals have been made as early as 1971 by Schenk [82], but the lack of an identified suture between the Anti-Atlas domain and the Meseta and the similarities in the Lower Palaeozoic stratigraphic record are quoted as evidence against such a scenario [49,51,52,71,73,75]; a recent confirmation of the Meseta block being of African affinity is provided by crustal xenoliths found in Triassic lamprophyres [31].…”

“…In conclusion, the Anti-Atlas was a fence-rider throughout, watching the action from a distance, not paying any tribute, nor suffering too much from the events going on all along the very active margins of Gondwana [49,62].…”

Palynologie et environnements des sédiments du Dévonien de Saïda (Algérie nord occidentale)

“…L'intrusion différenciée est mise en place à des niveaux structuraux superficiels atteignant l'épizone, voire l'anchizone, résultat d'un épaississement crustal peu développé (REMA- CI-BENAOUDA, 2005). Le caractère clastique à cachet turbiditique de la sédimentation dévonienne de la Meseta orientale marocaine et de la Meseta oranaise (Ghar Roubane, Tiffrit, Algérie), suggè-rent le développement d'un bassin turbiditique pendant le Dévonien (HOEPFFNER et al, 2005(HOEPFFNER et al, , 2006MICHARD et al, 2008). Leur âge, déterminé par les palynomorphes, est Praguien à Givétien-Frasnien (MARHOUMI et al, 1983).…”