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During the final stages of the Variscan orogeny, several subvolcanic dykes intruded throughout NW and SW Europe. In northern Portugal, the microgranite and lamprophyre of the Lamas de Olo region constitute a local manifestation of this magmatic event. To understand their petrogenesis, field, petrographic, and bulk-rock geochemical studies were undertaken. The lamprophyre was also analyzed for the Rb-Sr, Sm-Nd, and zircon U-Pb systematics. Mineralogically, the microgranite resembles alkali-feldspar granites, while the lamprophyre is a minette. Geochemically, the felsic dyke was probably derived from an evolved crustal source, possibly uncontaminated by mantellic or young crustal influences. The results suggest that the source is similar to that of the most evolved facies of the Lamas de Olo pluton. Structurally, the emplacement of the microgranite was presumably controlled by the regional WSW-ENE fracture system. On the other hand, lamprophyre emplacement is related to the regional NNE-SSW system. Fractional crystallization is likely to have conditioned the petrogenesis of the mafic dyke while crustal contamination probably played only a minor role. Several trace element ratios suggest that the lamprophyre resulted from low-degree melting of an enriched mantle source located in the lithospheric mantle. Source enrichment was presumably caused by subduction-related materials and metasomatism triggered by carbonate-rich fluids. When compared to other late-Variscan lamprophyres, the Lamas de Olo mafic dyke shares more similarities with the calcalkaline specimens of Western Europe. The present work corroborates previous studies concerning the hypothesis that late to post-Variscan lamprophyres may constitute a geodynamic pointer for a change in the tectonic regime.

Three of the largest granite porphyries of northern Portugal were studied to improve current knowledge on the regional felsic vein hypabyssal magmatism. All porphyries exhibit microcrystalline groundmasses of variable granularity (composed of quartz, K-feldspar, and muscovite), quartz, K-feldspar, plagioclase, biotite, and cordierite phenocrysts, antirapakivi and rapakivi feldspars, embayments in quartz, and enrichments in rare metal incompatible elements. The veins were emplaced along fractures generated during the last phase of the Variscan orogeny. Textural features were presumably conditioned by fast cooling, volatile loss, subsolidus annealing, and the magnitude of thermal contrasts at the time of emplacement. All veins were altered by subsolidus hydrothermal fluids, as suggested by several petrographic and geochemical evidence. The generation of mantled feldspars is probably related to isothermal decompression and magma mixing, which is compatible with the εNd i signatures (−3.76 to −4.40). Based on this research, both processes have contributed to the petrogenesis of the studied porphyries.

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