Basaltic magmatism occurs in the Hercynian foreland basin of the Western Moroccan Meseta as pillow lavas flows interbedded with “flysch” deposits and sills of dolerite and gabbro. A sedimentological and tectonic study shows that the deposition of the flysch, and thus the intrusion of the lava flows and sills, was controlled by the northwestward propagation of thrust‐related folds in the wedge‐top depozone of a syncontractional foreland basin system. The pillow lavas appear as either massive sheets of stacked lava flows or thin lava flows interlayered with the syntectonic turbiditic deposits. The sills are composed of several mafic units (up to six in the most evolved Marziqallal sill) cut through by granophyric veins, which can be interpreted as a result of in situ crystallization. The pillows lava basalts and the dolerites/gabbros are calc‐alkaline and cogenetic. A discussion of the possible mechanisms of magma production in subduction related orogens leads us to conclude that this foreland basin magmatism was generated in a retrolithospheric setting. A comparison with the other Early Carboniferous volcanic and plutonic rocks of the Western and Eastern Mesetas shows that calc‐alkaline foreland basin magmatism was widespread in the entire Mesetan domain and was probably a result of wet melting of the metasomatised mantle lithosphere of the overriding plate. Because the Moroccan Hercynides are likely to have been a result of continental subduction and the magmatism is observed at a distance of more than 500 km from the suture, it is suggested that the retroforeland basin magmatism was a result of either dehydration of a shallow dipping (∼15°) foregoing oceanic slab, or underplating of the continental lithosphere ending with slab breakoff beneath the foreland basin.

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International audienceThe origin and evolution of ultramafic (UM), mafic (M) and intermediate rocks emplaced within the metamorphic and anatectic series of the middle crust of the Variscan segment of the Pyrenees are defined in the light of new isotopic data U–Pb zircon ages, and Sr, Nd isotopic ratios. In the Gavarnie–Heas dome (central Pyrenees), ultramafic, mafic and intermediate rocks form three massifs several kilometers in size emplaced within the anatectic series: (i) the Gloriettes massif, which mostly consists of norites with enclaves of ultramafic rocks; (ii) the Troumouse massif, which comprises intermediate rocks (gabbro-diorite and diorite) with norite enclaves, and (iii) the Aguila massif, which consists of intermediate rocks with hornblendite enclaves. U–Pb zircon geochronology (first data for these rock types in the Axial Zone of the Pyrenees) revealed an age of 294 Ma for the diorite crystallization and correlatively for the crystallization of the anatectic granite. This new radiometric age allows us to suggest that the Variscan orogeny continued at least until the Early Permian and spread over around 30 Ma. The Nd and Sr isotopic compositions of all UM and M samples plot within the field of the continental crust. Two scenarios can explain the genesis and the emplacement of the components of the magmatic suite: i) evolution of mantle melts and contamination (AFC); ii) evolution of melts originating from a heterogeneous source (mantle + crust) at the local or regional scale. The strong crustal affinity of all UM and M rock types from Gavarnie–Heas leads us to favor the second scenario

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