Nouvelle approche géologique et géodinamique du Complexe Hydrothermal de Moulay Yacoub, bordure septentrionale du Sillon Sud Rifain

As águas termais de Moulay Yacoub surgem em formações miocénicas do Sulco Sul do Rife. São caracterizadas por forte mineralização, relacionada com a natureza do seu local de armazenamento e circulação em reservatórios de litologias variadas. Apresentam duas fácies químicas principais: uma Cl-Na, pouco diluída, e outra, Cl-Ca-Mg, dominada por águas imaturas. A comparção geoquímica e geotermométrica com outras fontes regionais sugere uma origem mais profunda que o reservatório liássico. A recente descoberta de extrusões de blocos de calcário liássico, de magmatitos paleozóicos, de metassedimentos e de grandes massas de doleritos triássicos, sugere a existência de formações permeáveis sob a cobertura margosa do Miocénico. Os acidentes profundos NE-SW, associados a um cavalgamento cego, sugerem uma relação estreita entre estas águas termais e as extrusões do soco ante-neogénicos. Durante a sua passagem para a superfície, as águas termais de Moulay Yacoub terão sido diluídas através de misturas ocorridas principalmente no reservatório liássico

Nouvelles observations dans le dépocentre volcano-sédimentaire carbonifère du Massif du Tazekka, Moyen-Atlas, Maroc : implications sur l'évolution géodynamique de la chaîne Hercynienne

A análise integrada das estruturas tectónicas e das fácies do Complexo Vulcano Sedimentar do Maciço de Tazekka sugere que este, à escala da grande bacia carbonífera de ante país da Meseta Oriental marroquina, corresponde a um depocentro ou sub bacia em compressão controlada pela propagação, para NW, de dobras de amortecimento do cavalgamento de Hajra Sbaa el Caid. As sequências tectono sedimentares, detrito conglomeráticas e/ou tufíticas, estão associadas a um magmatismo extrusivo com basaltos, andesitos, dacitos, riodacitos e riólitos homogéneos ou piroclásticos com blocos re sedimentados. Estes vulcanitos correspondem a uma sequência sub alcalina equivalente. As sequências calco alcalinas orogénicas características de ambientes de subducção. Estes resultados, assim como a comparação das idades de contracção regional na Meseta marroquina, permitem integrar o Maciço de Tazekka num contexto de wedge top deepzone dum sistema de bacias de ante país flexural, em compressão comandada pela progressão de duas sequências de cavalgamentos prógrados, de NW, desde o Fameno Tournaisiano ao Viseano sup. Terminal Westfaliano inf., da Meseta Oriental para a Meseta Ocidental, em Marrocos setentrional

Clinopyroxene trace element compositions of cumulate mafic rocks and basalts from the Hercynian Moroccan Central Meseta : petrogenetic implications

In the Fourhal foreland basin, in the north-eastern part of the Marrocan Central Meseta, mafic series are represented by basalts interbedded with Early Namurian turbidites and by numerous malfic sills, including the Marziqallal sill detailed here. The study of the trace element compositions of the clinopyroxenes, a ubiquitous mineral in the gabbroic sill and basalts, indicate that these two formations are derived from a similar parental magma. This magma evolved following a general fractional crystallization process involving the cumulation of clinopyroxene, then of ilmenite, occurring within the sill and having a leading role in the composition of the associated basalts. Calculated parental melts inferred from clinopyroxene analyses from the various cumulative units of the sill have trace element patterns similar to the one found for the basaltic flows. These patterns are compatible with magma and clinopyroxene compositions from a subduction-related geotectonic setting

Crustal anatexis in the Aouli-Mibladen granitic complex : A window into the middle crust below the Moroccan Eastern Variscan Meseta

The Moroccan Variscan belt comprises numerous granitoid bodies, which have been isotopically studied, but still lack a detailed petrogenetic model. The Variscan Aouli-Mibladen granitic complex in the Moroccan Eastern Meseta provides an excellent opportunity for studying the petrogenesis and the relationship with adjacent Cambro-Ordovician metasediments. This region exposes mainly M-to I-type metaluminous mafic to granitic bodies as well as migmatites and peraluminous S-type anatectic granites. An exceptional xenoliths and garnets cumulate deposit covers an area of ∼2 km 2 located NE of the complex. The S-type suite includes cordierite bearing microgranite dykes and two small two-mica leucogranitic stocks, crosscutting the eastern metamorphic aureole of the complex. Petrological analysis shows that biotite dehydration melting reactions produced anatectic melt and peritectic cordierite and garnet. Garnet shows complex zoning profiles, with typical prograde growth zoning in the core, and resorption and reprecipitation rims. Peritectic cordierite (X Fe = 0.37) is associated with restitic biotite (X Fe = 0.65), whereas abundant cotectic cordierite (X Fe = 0.65) belongs to the granites paragenesis (Bt + Kfs + Pl + Crd + Qtz). Garnet crystals are also frequently mantled by a retrograde cordierite type. Thermodynamic modelling shows that biotite dehydration melting took place under granulitic facies conditions (830–870 °C and 6 kbar), producing a significant amount of peraluminous melts. Their ascent and emplacement led to the S-type suite of the Aouli-Mibladen complex, including the local xenolith-cumulate deposit. We envisage a petrogenetic model during the Variscan orogeny, in which mantle derived mafic magmas stagnated in large reservoirs at 18–20 km depth, causing isobaric heating and partial melting of the surrounding metapelitic protolith. Differentiated M-I-type and S-type magmas were emplaced at higher levels concomitantly, with limited mixing and mingling during their final crystallization, at a depth of 9–10 km leading to contact metamorphism (600 °C, 3 kbar). These findings open a window into the hitherto unknown Moroccan Variscan mid-crust and permit to discuss the nature and age of the underlying basement terranes

Multi-stage metamorphism recorded in crustal xenoliths from Permian dykes of the region of Mrirt (Moroccan Central Massif)

The Permian magmatic rocks from Morocco contain crustal xenoliths that sample the Variscan crust in a context of widespread magmatism. A series of such xenoliths was collected in Permian dykes of the Central Massif, in the region of Mrirt. The metapelitic xenoliths are silica poor to intermediate (44 < SiO2 <57 wt%) and alumina-rich (17 < Al2O3 < 34 wt%) and are notably enriched in some HFSE (Nb, Ta, Ti) and some transition elements (Cr, V, W, Ni). Their petrographic evolution depicts a multi-stage evolution from an early, subsolidus, metamorphic history related to regional metamorphism, of which biotite, garnet and sillimanite are the witnesses toward a late thermal evolution coeval with the entrapment in the magma, marked by pervasive partial melting and development of peritectic spinel and cordierite together with K-feldspar and ilmenite. The overall presence of corundum, which relates to the high Al2O3 content, accounts for an initial stage of partial melting and magma escape, prior to the entrapment in the magma. Textural and chemical observation suggests further xenolith digestion and melt flux from the xenoliths toward the magma during ascent. Thermodynamic modelling allowing the determination of the pressure-temperature history of each xenolith shows that the initial pressure varies from ca. 1.5 to ca. 6 kbar, which, considering lithostatic pressure, corresponds to sampling depths of ca. 5–25 km. The temperatures recorded by the parageneses coeval with partial melting in the presence of spinel are in the range 800–900 °C whatever the pressure, which accounts for rapid heating due to thermal equilibration with the magma. U–Th/Pb dating of monazite by EMPA gives a poorly resolved Permian age of 293 ± 25 Ma for metamorphism in the xenoliths, in accordance with the stratigraphic age of the host rock. The pressure conditions are similar to those recorded for regional metamorphism in the other Variscan outcrops in Morocco, namely the Jebilet, the Rehamna and the Aouli-Mibladen granitic complex, while the maximal temperatures are much higher. The xenoliths thus appear as typical of the Late Variscan geological evolution of the deep crust in the Moroccan Mesetas, where abundant magmatism was responsible for local crustal heating of a crust previously affected by regional metamorphism

Multi-stage metamorphism recorded in crustal xenoliths from Permian dykes of the region of Mrirt (Moroccan Central Massif)

The Permian magmatic rocks from Morocco contain crustal xenoliths that sample the Variscan crust in a context of widespread magmatism. A series of such xenoliths was collected in Permian dykes of the Central Massif, in the region of Mrirt. The metapelitic xenoliths are silica poor to intermediate (44 < SiO2 <57 wt%) and alumina-rich (17 < Al2O3 < 34 wt%) and are notably enriched in some HFSE (Nb, Ta, Ti) and some transition elements (Cr, V, W, Ni). Their petrographic evolution depicts a multi-stage evolution from an early, subsolidus, metamorphic history related to regional metamorphism, of which biotite, garnet and sillimanite are the witnesses toward a late thermal evolution coeval with the entrapment in the magma, marked by pervasive partial melting and development of peritectic spinel and cordierite together with K-feldspar and ilmenite. The overall presence of corundum, which relates to the high Al2O3 content, accounts for an initial stage of partial melting and magma escape, prior to the entrapment in the magma. Textural and chemical observation suggests further xenolith digestion and melt flux from the xenoliths toward the magma during ascent. Thermodynamic modelling allowing the determination of the pressure-temperature history of each xenolith shows that the initial pressure varies from ca. 1.5 to ca. 6 kbar, which, considering lithostatic pressure, corresponds to sampling depths of ca. 5–25 km. The temperatures recorded by the parageneses coeval with partial melting in the presence of spinel are in the range 800–900 °C whatever the pressure, which accounts for rapid heating due to thermal equilibration with the magma. U–Th/Pb dating of monazite by EMPA gives a poorly resolved Permian age of 293 ± 25 Ma for metamorphism in the xenoliths, in accordance with the stratigraphic age of the host rock. The pressure conditions are similar to those recorded for regional metamorphism in the other Variscan outcrops in Morocco, namely the Jebilet, the Rehamna and the Aouli-Mibladen granitic complex, while the maximal temperatures are much higher. The xenoliths thus appear as typical of the Late Variscan geological evolution of the deep crust in the Moroccan Mesetas, where abundant magmatism was responsible for local crustal heating of a crust previously affected by regional metamorphism