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Morocco is a relevant place to study Mn deposits considering its multistage geodynamic story. In the last decades, several new studies significantly improved our understanding of various genetic types. Three main districts have been mined since the beginning of the 20th century: (i) Ouarzazate (Anti-Atlas), (ii) Bou Arfa (eastern High Atlas) and (iii) Imini-Tasdremt (High Atlas). The first and third are currently mined, accounting for the production of 80,000 tons Mn in 2018 (data from the Ministry of Energy, Mines and Sustainable Development of Morocco). The deposition of Mn spans over four main periods: Neoproterozoic, Jurassic, Upper Cretaceous and Cenozoic. (i) The Ouarzazate deposits are vein-type and stratiform Mn-Fe orebodies (42-48% Mn) closely associated to Neoproterozoic felsic volcanic and terrigeneous series. It is the largest Mn field in Morocco (>90x60 km). Stratiform orebodies clearly improve the mining potential. The Mn-bearing assemblage includes braunite, cryptomelane, hollandite, hausmannite and pyrolusite in a hematite, goethite, barite, quartz, dolomite and calcite gangue. The formation model implies a polycyclic epithermal and epigenetic Mn accumulation during and at the final stage of the Neoproterozoic volcanic activity at ~580 Ma. Tectonic of the Neoproterozoic Ouarzazate basin would be of primary order in delimiting the number and regional extension of lodes. (ii) The Bou Arfa Mn deposit is hosted in Sinemurian dolostones, as stratabound, run-type and lenses Mn orebodies crisscrossed by late veins hosting the high-grade pyrolusite ore (33-82% Mn). The ore formation follows a sedimentary-diagenetic model driven by three dolomitization episodes after the Sinemurian sedimentation, similar to other MVT of the Atlas range. The concentration of Mn in a narrow area of about 10 km2 is due to the geometry of the Bou Arfa basin and its position above basement paleohighs acting as a threshold for marine inputs during transgression/regression intervals. The primary manganite-hausmannite ore was transformed into pyrolusite during burial of the Mn-rich sediments. (iii) The Imini-Tasdremt district is the most economically important of Morocco providing the highest Mn grade (74-92% Mn) due to two stratabound pyrolusite-bearing orebodies hosted in the ~10-20 m thick Cenomanian-Turonian dolostone. A metallurgical third ore (40-48% Mn) occurs in relics of a paleosurface in the uppermost dolostone and is composed by coronadite group minerals. Although the pyrolusite ore is restricted to the 25-30 km Imini Mn belt, the metallurgical ore has a larger extension of ~100 km and may extend across the Atlas belt. New dating of K-Mn oxides (40Ar-39Ar) and goethite (U-Th)/He dating suggest that this geometric distribution is materialized by different formation age: the upper coronadite level is late Cretaceous, whereas the pyrolusite ores are Cenozoic, indicating the importance of local processes. Goethite ages cover a period of ~40 Ma since Turonian, involving long mineralization processes. The Atlas geodynamic played a significant role in the metallogenesis of these karst-hosted accumulations since late Cretaceous times.

International audience; Morocco is a relevant place to study Mn deposits considering its multistage geodynamic story. In the last decades, several new studies significantly improved our understanding of various genetic types. Three main districts have been mined since the beginning of the 20 th century: (i) Ouarzazate (Anti-Atlas), (ii) Bou Arfa (eastern High Atlas) and (iii) Imini-Tasdremt (High Atlas). The first and third are currently mined, accounting for the production of 80,000 tons Mn in 2018 (data from the Ministry of Energy, Mines and Sustainable Development of Morocco). The deposition of Mn spans over four main periods: Neoproterozoic, Jurassic, Upper Cretaceous and Cenozoic. (i) The Ouarzazate deposits are vein-type and stratiform Mn-Fe orebodies (42-48% Mn) closely associated to Neoproterozoic felsic volcanic and terrigeneous series (Choubert and Faure-Muret, 1973). It is the largest Mn field in Morocco (>90x60 km). Stratiform orebodies clearly improve the mining potential. The Mn-bearing assemblage includes braunite, cryptomelane, hollandite, hausmannite and pyrolusite in a hematite, goethite, barite, quartz, dolomite and calcite gangue. The formation model implies a polycyclic epithermal and epigenetic Mn accumulation during and at the final stage of the Neoproterozoic volcanic activity at ~580 Ma. Extensional tectonics of the Neoproterozoic Ouarzazate basin would be of primary order in delimiting the number and regional extension of lodes. (ii) The Bou Arfa Mn deposit is hosted in Sinemurian dolostones, as stratabound, run-type and lenses of Mn orebodies crisscrossed by late veins hosting the high-grade pyrolusite ore (33-82% Mn). Ore formation follows a sedimentary-diagenetic model driven by three dolomitization episodes after the Sinemurian sedimentation, and an epigenetic stage similar to other MVT of the Atlas range (Lafforgue et al., 2021). The concentration of Mn in a narrow area of about 10 km 2 is due to the geometry of the Bou Arfa basin and its position above basement paleohighs acting as a threshold for marine inputs during transgression/regression intervals. The primary manganite-hausmannite ore was transformed into pyrolusite during burial of the Mn-rich sediments.

International audience; 447Petrography and origin of the Mn(-Pb) Tasdremt deposit (High Atlas, Morocco)Augustin Dekoninck∗1, Gilles Ruffet 2, Mohamed Magoua 3, Yves Missenard 4, Oriane Parizot 4,AbdellahMouttaqi 3, Omar Saddiqi 5, Johan Yans 11 Université de Namur, Département de Géologie, ILEE – Namur – Belgique2 Université de Rennes 1, Géosciences Rennes – CNRS UMR 6118 – France3 Office National des Mines et des Hydrocarbures, Rabat (ONHYM) – Maroc4 Université Paris Sud XI, Orsay (GEOPS) – 8148 – France5 Université Hassan II, Géosciences, Casablanca – MarocThe Tasdremt manganese deposit is located in the southern foreland of the High Atlas at 70 km to the E of Taroudant, and 90 km to the SW of the Imini manganese district. The manganese ores are located in the Cretaceous strata of Tasdremt [W] and Aoufour [E]. The Cretaceous sedimentation is a succession of i) a 0–30 m thick detritic serie (red clays, sandstones and conglomerates, infra-Cenomanian), ii) a 0–20 m thick dolostone Cenomanian-Turonian in age, and iii) a Senonian detritic succession (20–50 m thick) composed of dolomitized sandstones and conglomerates interbedded with sandy dolostones. The Cenomanian-Turonian dolostone is subdivided into a yellow/gray dolostone at the base, which is covered by ii) a pinkish/white fossiliferous dolostone, the top being brecciated in contact with the Senonian conglomerates. The variable thickness of the whole Cretaceous serie is attributed to paleotopographic hights of the Cambrian dolostones. These rocks were deformed during a post-Cretaceous tectonic phase, probably the Late Eocene Atlasic one, inducing thick-skin thrusting of Cambrian dolostones over meso-cenozoic series. The present study shows that the stratigraphic position and the lateral extension of the manganese levels are quite variable along the district. The main orebeds are exposed at the top of the yellow and fossiliferous dolostone, while other manganese occurrences are located at the top of the infra-Cenomanian sandstones, at the base of the Senonian conglomerates and dolostones. X-ray diffraction points out that the ore is composed of hollandite group minerals [(K,Ba,Pb)Mn8O16], with only small amounts of lithiophorite. Pyrolusite is nearly absent. Petrographic observations indicate that hollandite group minerals replace dolomite crystals, and fill open cavities in the dissolved dolostone, while brecciated fragments of the Mn-ore, dolomite and quartz at the top of the fossiliferous dolostone are cemented by a late calcite. This breccia is then covered by the Senonian conglomerates. This suggests that the mineralization postdates the dolomitization of the host dolostone, but predates the deposition of the Senonian sediments. This could be linked to the post-Turonian karstification period. However, the occurrence of mineralized Senonian sandstones and dolostones, as well as Mn-ore cemented by colloform hol- landite group minerals or Mn-ore in tectonic joints may indicate a second mineralization stage, postdating the Cretaceous sedimentation.

International audience; Over the past 10 years, the effects of radiationdamage on helium diffusion kinetics werediscovered and led to significant improvements ofthe (U-Th-Sm)/He thermochronomeric system.Nevertheless, helium retention rate and closuretemperature in apatite are still debated, mostlybecause the physical nature of these defects, andtheir ability to trap helium are still unknown.Based on recent experimental analyses andquantum calculation, Gerin et al. (2017) predicthelium diffusion properties in damaged apatite. Inthis contribution, we present a new dataset ofapatite He and AFT ages, from a 300 Ma pluton(French Brittany). Using the new model, wequantify trapping behaviour in terms of energy.The AHe date dispersion for single grain withsimilar eU content may be explained by avariation in the trapping ability. We additionallypropose that damage connect and cluster for highdamage content leading to a decrease of retention.Gerin et al., 2017. Influence of vacancy damage on Hediffusion in apatite, investigated at atomic to mineralogicalscales. Geochim. Cosmochim. Acta. 197, 87-103

This thesis focuses on the study of vertical movements and the characterization of the main processes controlling them in an intraplate mountain belt. The mechanisms at the origin of the relief evolution are numerous and still poorly known. The High Atlas belt of Morocco is situated at more than 600 km of the Africa-Europe plate boundary, and supports the second highest peak of Africa (Jebel Toubkal, 4165 m). The lack of a significant crustal root under the belt, a consequence of limited shortening (~20 km), implies that another process takes place to explain such elevations. Lithospheric cross-sections allow us to show that a lithospheric thinning explain 1000 m of topography in the Anti-Atlas, the Central High Atlas, the Middle Atlas. Some of the foreland basins are also affected, like the Souss, Ouarzazate and Missour basins. The thinned area is an elongated stripe running North East / South West and crossing over the main structural domains of Morocco and probably the Africa-Europe plate boundary.The second mechanism explaining the High Atlas topography is the crustal shortening. We present a structural analysis on the basis of field data in the Marrakech High Atlas. The constrated mechanical stratigraphy is described, and numerous potential décollement levels are identified. They are mostly developed in the Visean, Cambrian, Triassic and Senonian units. The complex heritage of this area, situated between the Triassico-Liassic Atlantic and Tethyan rifts, controls their activation on the belt borders. They trigger the formation of various structures, such as tectonic wedges, rabbit ears folds, imbricate fans... A basal rigid group is distinguished, including the Precambrian rocks and locally the Paleozoic and Triasic series. A complete cross section of the belt is presented. The chronology of the deformation and the age of the lithospheric thinning are finally discussed. We propose a scenario of the foreland evolution in the light of the available geological data combined with new results of fission track thermochronology. A first shortening phase occurred during Upper Eocene to Oligocene. The lithosphere is thinned between the Lower and the Middle Miocene, and a main erosionnal event affects the belt and its foreland. Finally, the crustal shortening starts again during Plio-Quaternary., L'objectif de cette thèse est l'étude des mouvements verticaux et la caractérisation des processus à l'origine de ces mouvements au sein d'une chaîne de montagnes intracontinentale. Les mécanismes contrôlant l'évolution de la topographie sont nombreux et encore mal connus. La chaîne du Haut Atlas marocain est située à plus de 600 km de la limite de plaque Afrique-Europe et supporte pourtant le deuxième sommet d'Afrique (Jbel Toubkal, 4165 m). L'absence de racine crustale développée sous la chaîne, conséquence d'un taux de raccourcissement assez faible (~20 km), implique donc l'existence d'un autre processus permettant de maintenir une telle topographie. La réalisation de profils géophysiques nous permet de montrer qu'un amincissement lithosphérique provoque un soulèvement d'environ 1000 m dans l'Anti-Atlas, le Haut Atlas Central, et le Moyen Atlas. Certains bassins d'avant-pays sont aussi affectés, comme les bassins du Souss, de Ouarzazate ou de Missour. La zone amincie est une bande d'orientation Nord-Est / Sud-Ouest recoupant les principaux domaines structuraux marocains et probablement lalimite de plaque Afrique-Europe.Le raccourcissement crustal est le deuxième mécanisme à l'origine du relief de cette chaîne. Une analyse structurale sur la base des données de terrain dans le Haut Atlas de Marrakech nous a permis de montrer l'existence d'une stratigraphie mécanique contrastée. Plusieurs niveaux de décollements potentiels y sont identifiés en particulier dans le Viséen, le Cambrien, le Trias et le Sénonien. L'héritage complexe de cette région, située à la limite entre les rifts Triasico-Liasiques Atlantique et Téthysien, contrôle leur activation sur les bordures de la chaîne. Celle-ci entraîne la formation de structures variées : zones triangulaires, plis secondaires (« rabbit ears »), imbrications. Un groupe basal rigide est distingué. Il inclut le Précambrien, et localement le Paléozoique et le Trias. Une coupe complète de lachaîne est présentée. La chronologie de la déformation et l'âge de l'amincissement de la lithosphère sous la chaîne sont finalement discutés. Une analyse détaillée de la géologie de l'avant-pays sud du Haut Atlas de Marrakech est combinée aux résultats obtenus par comptage de traces de fissions pour proposer un scénario d'évolution. Une première phase de raccourcissement est identifiée à l'Eocène Supérieur – Oligocène. Au Miocène Inférieur – Moyen, la lithosphère est amincie et une phase de dénudation affecte l'ensemble de la chaîne et son avant-pays. Enfin, une dernière phase de raccourcissement a lieu au Plio-Quaternaire.

International audience; The Moroccan lithosphere is characterized by an anomalously thinned area, located beneath the Atlas domains, which forms a singular narrow NE-SW directed strip overlain by Cenozoic alkaline volcanism. The origin of this thinning and volcanism is still a matter of debate. The proposed models invoke processes either related to the Mediterranean slab or mantle plumes. Herein, we propose an alternative Edge-Driven Convection (EDC) model involving small-scale convection at the boundary between the West-African craton and the Atlas lithosphere. Our comparison of the Atlas lithosphere velocity and volcanism episodes during the last 80 Ma points out that volcanism occurs when plate moves at velocities c.

The method for thermal modelling, the thermal modelling for all samples and the relationship between apatite chemistry.