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Present structure of the Moroccan Variscides in map view (A) and tentative restoration at ca. 360 Ma, before the Variscan events (B).
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This work is based on the compilation and re-evaluation of the most significant data, either personal or from the literature, concerning the Moroccan Variscides. The latter constitute the only, moderately disturbed or even undisturbed part of the South-Western Branch of the Variscan Belt, facing directly NW Gondwana. They include two orogenic segme...
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The Betics and Rif cordillera constitute the northern and southern segments of the Gibraltar arc. Two different fold-and-thrust
belts, deriving from the South Iberian and Maghrebian paleomargins respectively, developed in front of this orogenic system.
By contrast, the Flysch Trough units and the overlying Alboran crustal domain (internal zones), w...
Citations
... From west to east, they are Iberian Massif, Pyrenean Axial Zone, Armorican Massif, Massif Central, Rhenish Massif. Vosges-Schwarzwald massifs, and Bohemian Massif [9,11,55,56]. ...
... The genesis of these granitoids may be related to either the interaction of mantellic magma with crustal rocks or with the partial fusion of exclusively crustal sources. The present-day structure of the Moroccan Variscan belt is mainly the result of oblique convergence between the Gondwana and the Laurasia supercontinents during the late Palaeozoic (e.g., Ribeiro et al., 1979;Matte, 2001;Michard et al., 2010;Martínez-Catalán et al., 2021;Arenas et al., 2021;Chopin et al., 2023). This chain, located in northwest African Variscan-Alleghanian orogen, is subdivided into different segments (Fig. 1). ...
In the northern part of the Marrakech High Atlas (MHA), along the southern Variscan segment of the Western Meseta, a Variscan granitic intrusion crops out, intruding metasediments and meta-volcanosedimentary rocks of Early Cambrian to Ordovician age. A new whole-rock Rb-Sr isochron age of 268 ± 9 Ma for the granite, combined with a previously published whole-rock Rb-Sr radiometric dating (271 ± 3 Ma), reveals a post-kinematic (tectonic) character with regard to the main Variscan deformational event, belonging within the tectonic context of the Moroccan Variscan orogenic belt. Geochemically, the Azegour intrusion is metaluminous to peraluminous and exhibits a calc-alkaline affinity with a ferruginous composition. The massif shows an extremely differentiated character (SiO2 = 77.53–78.14 per cent), K2O and high total alkali contents, FeOt/(FeOt + MgO) and Ga/Al ratios, which have typical characteristics of an A-type granite. In addition, the granite contains high concentrations of LREE (LaN/SmN= 7.9–13.67) relative to HREE (LaN/YbN= 4.81–11.61) and a well-defined Eu negative anomaly (Eu/Eu* = 0.44–0.75). The granitic samples exhibit a strong enrichment of the most incompatible elements (RbN/YbN = 69.84–159.98) and a strong depletion of Ba, Sr, Eu, Nb, P and Ti. These characteristics are similar to those of A1-type granites. The absence of mineralogy typical of an S-type granite, combined with its weakly peraluminous character [A/CNK (molar Al2O3/CaO+Na2O+K2O) = 1,013–1,045], suggest that there is little or no significant involvement of supracrustal sources in the petrogenesis of the intrusion studied. Despite the strongly differentiated character of Azegour granitic rocks samples, their multi-element patterns shows many similarities to those of I-type granitoids, which has led to postulate that the parental liquids of A1-type were derived from partial melting of mafic magmas. The representative samples studied show less depleted εNd(t = 270 Ma)values of –0.94 to –4.85 and lower positive to slightly negative εSr(t = 270 Ma) values of –1.45 to 9.32. The isotopic data suggest that the Azegour granite was emplaced 270 myr ago, apparently generated by partial melting of a mafic/intermediate magma source in the lower crust as a result of the underplating of the asthenosphere mantle-derived Oceanic Island Basalt-like magmas. Alternatively, their isotopic signatures also can be attributed to the interaction and/or hybridisation of basaltic liquids derived from the mantle with these lower crust materials. The generated parental magma probably occurred at deep structural levels and involved fractional crystallisation processes by the separation of a mineralogical association composed of plagioclase + potassium feldspar ± biotite ± amphibole ± sphene ± apatite. The whole-rock Rb-Sr age of 268 ± 9 Ma, whole-rock geochemistry and Sr-Nd isotopic compositions of εNd(t = 270 Ma) and εSr(t = 270 Ma), combined with fieldwork data, suggest that the Azegour granite was emplaced.
... These areas underwent a sub-meridian syn-schist folding phase, associated with epizonal metamorphism of the post-upper Visean age, followed by sub-parallel shearing at S1 [40,41]. However, there is also the existence of a peri-plutonic metamorphism that developed around granite intrusions. ...
... This corroborates the geodynamic models proposed to explain the evolution of the Meseta from Upper Devonian to Lower Permian. The eastward subduction of the Rheic Ocean, leading to the formation of fore-and back-arc basins in the Mesetian block between the 420 and 330 Ma models [40,95,96], corroborates the Evolution model of the Meseta during the Carboniferous proposed by Essaifi et al. [97], which involves westward subduction followed by a slab breakoff, leading to upwelling of hot asthenospheric currents and eroding the litho-sphere. ...
The Sidi Bou Othmane (SBO) pegmatite district is situated in the Central Jebilet massif, Western Meseta domain, Morocco. The SBO district is hosted essentially in a volcano-sedimentary series composed of Late-Devonian Sarhlef shales. Pegmatite bodies crop out as dykes, which are oriented from N-S to E-W and are generally variably deformed with ductile and/or brittle structures with ante, syn- or post-kinematic criteria. Petrographic observations of pegmatite dykes show that feldspars (i.e., albite, microcline) are the most abundant mineral phases, followed by quartz and micas, with tourmaline and accessory minerals such as garnet, and zircon also featuring heavily, as well as secondary minerals such as clinochlore, sericite, and illite. The geochemical study of the SBO pegmatites indicates that they have mainly S-type granitic compositions, which are peraluminous granites with calc-alkalic affinities. The study of trace elements indicates that SBO pegmatites were formed in post-orogenic syn-collision context during the Variscan orogeny by the partial melting of argilliferous sediment. They can be ascribed to the muscovite-bearing pegmatite; moreover, they have good potential regarding ceramics. They also contain minerals, such as feldspar, which have been recently assessed as critical raw materials by the European Union.
... Chopin et al., 2014;Wernert et al., 2016) defined both a transpressional and transtensional tectonic framework combined with an intracontinental strike-slip shear network (Elter et al., 2020;Hoepffner et al., 2006). The Mauritanide segment of the Variscan orogeny in North Africa is predominantly exposed in Morocco and forms the Moroccan Variscides at the NW margin of Gondwana (Hmich et al., 2006;Michard et al., 2010b). The Mauritanides can be interpreted as the southwestern prolongation of its European counterpart (Chopin et al., 2014;Elter et al., 2020;Hoepffner et al., 2006;Hoepffner et al., 2005;Michard et al., 2010a;Michard et al., 2008;Michard et al., 2010b;Wernert et al., 2016;Zouicha et al., 2022). ...
... The Mauritanide segment of the Variscan orogeny in North Africa is predominantly exposed in Morocco and forms the Moroccan Variscides at the NW margin of Gondwana (Hmich et al., 2006;Michard et al., 2010b). The Mauritanides can be interpreted as the southwestern prolongation of its European counterpart (Chopin et al., 2014;Elter et al., 2020;Hoepffner et al., 2006;Hoepffner et al., 2005;Michard et al., 2010a;Michard et al., 2008;Michard et al., 2010b;Wernert et al., 2016;Zouicha et al., 2022). ...
... Accordingly, Paleozoic massifs of the WM (i.e. Jebilet, Rehamna and Central Massif) are split by the WMSZ into segments belonging to the coastal block (Western Jebilet and Western Rehamna) and the central zone (Eastern Jebilet, Eastern Rehamna and the Central Massif) ( Fig. 1; Barbero et al., 2011;Chopin et al., 2014;Delchini et al., 2016;Essaifi and Hibti, 2008;Hoepffner et al., 2006;Hoepffner et al., 2005;Michard et al., 2008;Michard et al., 2010b;Saddiqi et al., 2009). ...
Although Pangea as Earth’s youngest supercontinent has continuously served as a pivotal reference mark in paleogeographic reconstructions, its assembly is still a matter of debate. This is mainly due to poor paleomagnetic data coverage for Permian times for Africa, core element of Pangea. Paleomagnetic data for Adria, thought to be the African promontory in the Permian, yield paleolatitudes which when compared to the European data set result in a significant continental overlap and seem to confirm the original Pangea B concept of Irving (1977). In order to improve the paleomagnetic data base for Africa, volcanic and sedimentary rocks were sampled in the Permo-Carboniferous basins of Morocco yielding a total of 97 sites and 615 samples. Rock magnetic studies are diagnostic for magnetite and hematite in various proportions as main carriers of the paleomagnetic signal. After removal of low and intermediate coercivity/blocking temperature components a characteristic component of magnetization pointing to the SE with declinations strung out along a small circle from 107° to 182° and with inclinations around -7° after tectonic correction was identified in 76% of the samples. In nine out of the ten basins studied, positive inclination only fold tests support the
primary character of magnetization. Furthermore, three reversals were identified at the basins of M’Tal, Chougrane and Souk El Had Bouhsoussene lending further support to our interpretation. VGPs are distributed along a NE-SW trending small circle band intersecting the Late Paleozoic segment of the Gondwana APWP with a rotation pole located in the sampling area. The resulting paleolatitudes yield a position of the Meseta block close to the
paleo-equator at ~280 Ma. The widespread presence of vertical axis rotations in the Meseta basins on the other hand, could be related to proposed intra-Pangea shear zones and would
provide additional constraints on the extent of such shear zones towards the northern margin of Gondwana. However, tectonic models based on vertical axis rotations in this region need to
be treated with caution, since the timing of these rotations remains ambiguous with the current data set. Using our paleomagnetic data from the Meseta block as representative for Gondwana, a large latitudinal overlap between Gondwana and
Laurussia is not required.
... Structurally, the Western High Atlas belongs to the Variscan belt and is comprised between two major dextral shear zones along the NE-SW trending structures ( Fig. 1) [27]. To the north side, the Imi-n'Tanout fault constitutes its northern side with the Haouz basin and the Tizi-n'Test shear zone limits it at the southern flank with the Souss basin ( Fig. 1) [22], [26], [34]. According to [22] and [26], the Variscan orogeny is characterized by three deformational events (D1, D2 and D3). ...
Purpose. In this paper, we discuss the genetic model and emphasize many pending issues on the carbonate replacement textures of the Amensif Zn-Pb-Cu-Ag±Au-Bi deposit (the Western High Atlas, Morocco), the source of metal and the possible contribution of the Azegour granite to this ore genesis. Methods. This study is based on geological mapping, drill core and petrography analysis in combination with ICP-AES, XRD, and SEM data. Findings. The detailed mineralogy consists mainly of sulfides and sulfosalts. The main ore minerals include arsenopyrite, pyrite, sphalerite, chalcopyrite, galena and bismuthinite. Mineral inclusions related to isomorphic sulfosalts are found in galena and/or chalcopyrite. They include matildite, galenobismutite, pavonite, cosalite, schirmerite, krupkaite, ramdohrite, wit-tichenite, emplectite, luzonite, gustavite, hedleyite, krennerite, wittite, freibergite, tetrahedrite, tennantite and native bismuth. The supergene minerals are anglesite, covellite, malachite, azurite and goethite. In addition, specific replacements are observed between dolomites and sulfides, indicating an interaction between hydrothermal fluid and host rocks. Four ore stages have been identified based on the relationship between mineral phases and ore-forming conditions. The results of this study indicate that Ag and Au precipitation is controlled by the BiTe -Pb-S system, while enrichment in Bi, Te and Se sulfosalts and Bi-telluride indicates a magmatic source of the ore-forming fluid. Originality. The study delves into the genetic model of the Amensif Zn-Pb-Cu-Ag±Au-Bi deposit in the Western High Atlas , Moroc-co, with a focus on carbonate replacement textures, while also exploring its classification as either a carbonate replacement deposit or a skarn deposit. Practical implications. Mineral textures are indicators of the replacement process in the Amensif Zn-Pb-Cu-Bi-Ag±Au carbonate replacement deposit (the Western High Atlas, Morocco). The results obtained from this research paper can be used as a powerful tool in mineral exploration of the Western High Atlas.
... Folding and faulting of the Paleozoic series are attributed to the Variscan and partially Alpine orogenies [37,39,[43][44][45][46]. The current elevation of the eastern Anti-Atlas, reaching approximately 2700 m in the Jbel Amalou n'Mansour of the Saghro Massif, is due to the latest Atlasic-Alpine shortening [47]. ...
... Geological map of the Anti-Atlas belt[37,44,72]. ...
The Ougnat Massif of the eastern Anti-Atlas (Morocco) hosts barite and sulfide vein-type deposits of vital economic importance. With over 150 mineralized structures reported in the Ougnat Massif, the ore-bearing ones are predominantly composed of barite, quartz, calcite, and minor portions of sulfides. The mineralized veins are driven by NW-SE and NE-SW to E-W oblique-slip opening faults that cross both the Precambrian basement and its Paleozoic cover. The mineralized structures occur as lenses and sigmoidal veins that follow stepped tension fracture sets oblique to the fault planes. These geometries and kinematic indicators of these structures point to a predominantly normal-sinistral opening in a brittle-ductile tectonic setting. The S isotopic compositions of barite from the Ougnat Massif (+10.8 to +19.5‰) fall mostly within the range of δ34S values of Late Triassic to Jurassic seawater, thus suggesting that some of the SO2− in barite comes from seawater sulfate. This range of δ34S values also corresponds approximately to the hydrothermal barite context. The 87Sr/86Sr ratios of barite, which range from 0.710772 to 0.710816, lie between the radiogenic strontium isotopic compositions of deposition by hydrothermal solutions, and also coincide with the non-radiogenic isotopic signature of Triassic to Jurassic seawater. Based on a fluid inclusions study, the ore-forming fluids were a mixture of two or more fluids. A deep hot fluid with an average temperature of 368 °C leached the granodiorites and volcanic-sedimentary complex of the Ouarzazate Group. This fluid provided the hydrothermal system with most of the Ba, radiogenic Sr, and some of the dissolved S. A second, shallow fluid with an average temperature of 242 °C was derived from Late Triassic to Jurassic seawater. The barite mineralization of the Ougnat Massif constitutes a typical example of vein-type mineralization that occurred along the northern margin of the West African Craton and regionally tied to the central Atlantic opening.
... Despite the thorough knowledge of the regional evolution of this important area, many sub-basins remain insufficiently investigated and poorly understood. Studies in the Moroccan segment have mainly focused on the crystalline basement of the Oulad Dlim Massif and the Reguibat Ridge (Fig. 1d), (Villeneuve et al., 2006;Gärtner et al., 2013Gärtner et al., , 2016aVilleneuve et al., 2015;Michard et al., 2010Michard et al., , 2023Haissen et al., 2018;Bea et al., 2020;El Amraoui et al., 2023;Malainine et al., 2023) and their offshore component (Hafid et al., 2006;Neumaier et al., 2016;Uranga et al., 2022;Galhom et al., 2022). The presence of normal faults and the rifting-drifting evolution of the region have been highlighted in these studies. ...
The Senegal-Mauritanian Basin onshore is the largest among the northwest African Atlantic margin basins, covering approximately 350,000 km2 and extending from Morocco to Guinea Bissau. Although valuable information is provided on the Senegalese part, data on other parts of the basin are scarce. The study aims to visualise the subsurface structure and describe the distribution patterns of Meso-Cenozoic deposits in the Moroccan portion of the Senegalo-Mauritania basin. The dataset integrates information from 750 vertical electrical soundings, hydrogeological drilling data, and wireline logging into a Geographic Information System (GIS) platform and 3D modelling software. A new three-dimensional model has been created to represent the topmost layer of the Palaeozoic substratum. Additionally, thickness maps and geo-electric profiles have been developed for distinct geo-electric intervals, including the lower, middle, upper, and surface layers. The study presents the geometric properties of two aquifers, namely, the ''upper and lower'': the Continental Terminal sandy and sandstones, dating back to the upper Miocene to Pliocene period, and the Paleocene sand to shaly sand. The upper aquifer has a thickness of 20 m in the eastern region, whereas it thickens to nearly 100 m towards the west, approaching the coastline. Similarly, the lower aquifer's thickness ranges from 100 m to 400 m in the same direction. The resistivity values range from 5 to 240 Ω m, providing an average of 120 Ω m. Four discontinuities have been identified in the sections, which may indicate lateral facies modifications or synsedimentary faults, correlating with Atlantic margin structuration and Meso-Cenozoic sea-level variations. The parameters' range for various mappings, models, and quantitative descriptions of reservoir properties. The new structural and hydro-stratigraphic model provides novel insights for researching this critical area.
... The phosphate series of the BouCraa deposit belongs to the Tarfaya-Laayoune-Dakhla basin. The latter is bordered to the east by the Reguibat Shield which consists of granitoids, migmatites, and metamorphic rocks of Precambrian basement and Paleozoic detrital deposits, and to the northeast by the Anti-Atlas Mountains formed by Precambrian granitoids and rhyolites and Paleozoic carbonates and detrital deposits (Michard et al., 2010). The montmorillonites come from the Western Anti-Atlas Mountains and the Reguibat Shield by the reworking and transport of soils and sediments loaded with silica and basic cations, exposed to a hot and semi-arid climate. ...
Book Subtitle
Proceedings of the 3rd Conference of the Arabian Journal of Geosciences (CAJG-3)
Editors
Federico Lucci, Domenico M. Doronzo, Jasper Knight, Anna Travé, Stefan Grab, Amjad Kallel, Sandeep Panda, Helder I. Chaminé, Jesús Rodrigo-Comino, Sami Khomsi, Santanu Banerjee, Broder Merkel, Haroun Chenchouni
... Ce modèle a ainsi été comparé, avec un certain succès, avec l'évolution de la chaîne varisque en termes de déformation et d'évolution thermique. Cependant, le champ de déformation dans la chaîne varisque montre que les domaines en raccourcissement ne sont pas restreints au coeur de l'arc (voir figure 2.28) au Carbonifère terminal, puisqu'ils sont observés dans la chaîne alléghénienne (Michard et al. 2010 ;Delchini et al. 2018), ainsi que dans les Pyrénées et le système Maures-Corse-Sardaigne Casini et al. 2015). En outre, le modèle de flambage à l'échelle lithosphérique pose des questions mécaniques de premier ordre qui ne sont pas résolues (Schellart et al. 2004 ;Rosenbaum 2014). ...
La chaîne varisque en France 2 traite de l’histoire géologique et de l’évolution des idées concernant la chaîne varisque en France.Cet ouvrage propose une analyse des évènements magmatiques, métamorphiques et tectoniques tardifs ainsi que des archives sédimentaires, documentant ainsi le démantèlement de la chaîne varisque au Carbonifère supérieur.La synthèse des données pétro-chronologiques met en évidence une évolution de haute-température, associée à un magmatisme impliquant une source mantellique enrichie en matériel crustal. L’intégration des marqueurs structuraux souligne un épisode de restructuration tardi-orogénique majeur affectant une lithosphère faible. La synthèse des données sédimentaires permet de reconsidérer l’histoire de l’orogène sous le prisme de l’évolution des bassins. Enfin, la conclusion générale de l’ouvrage met en valeur les questions thématiques posées par l’orogénèse varisque.
... This corroborates with the geodynamic models proposed to explain the evolution of the Meseta from Upper Devonian to Lower Permian. The Eastward subduction of 29 the Rheic Ocean leading to the formation of fore-and back-arc basins in the Mesetian block between 420 and 330 Ma model [92,93,94] corroborates also with the Evolution model of the Meseta during the Carboniferous, proposed by Essaifi et al., [95] involving west-ward subduction followed by a slab breakoff leading to upwelling of hot asthenospheric currents eroding the litho-sphere. ...
The Sidi Bou Othmane (SBO) pegmatite district is in the Central Jebilet massif, Occidental Meseta domain, Morocco. The SBO district is hosted essentially in a volcano-sedimentary series composed of the Late-Devonian Sarhlef shales. Pegmatite bodies crop out as dykes, which are oriented from N-S to E-W and are generally variably deformed with ductile and/or brittle structures with ante, syn- or post kinematic criteria. Petrographic observations of pegmatite dykes show that feldspars (i.e., albite, microcline) are the most abundant mineral phases, followed by quartz, micas, with tourmaline and accessory mineral as garnet, and zircon and secondary minerals as clinochlore, sericite, and illite. The geochemical study indicates that, according to the major pegmatite elements dykes of SBO have mainly a S-type granitic composition and are peraluminous granite with calc-alkalic affinity. The study of trace elements pointed out that SBO pegmatite formed under post-orogenic syn-collision context during the Variscan orogeny, by the partial melting of argilliferous sediment and can be ascribed to the muscovite-bearing pegmatite; moreover, they have a good potential on ceramic and contain minerals, such as feldspar, recently assessed as Critical raw materials by European Union.
