Late-Variscan emplacement and genesis of the Vieira do Minho composite pluton, Central Iberian Zone: Constraints from U–Pb zircon geochronology, AMS data and Sr–Nd–O isotope geochemistry

Abstract In the Central Iberian Zone synorogenic (syn- and late-D3, the last deformation phase) composite batholiths of biotite-rich granitods with peraluminous character are well represented. We report here U–Pb zircon and monazite ages, geochemical, Sr–Nd–O isotopic data and Anisotropy of Magnetic Susceptibility (AMS) studies for the late-D3 Vieira do Minho pluton, in northern Portugal. AMS reveals the paramagnetic behaviour of these granites and the magnetic fabric enhances the major role of NW–SE regional anisotropies on controlling the ascent and emplacement of the magmas. Magnetic anisotropy and medium temperature microstructures also point out the evolution of regional tectonics during crystallization of the magma. U–Pb zircon and monazite analyses yield consistent ages of 310 ± 2 Ma and 312 ± 2 Ma, interpreted as emplacement age. The Vieira do Minho pluton consists of two peraluminous monzogranites, the VMG and the MRG. Both have similar εNd values (VMG = − 5.2 to − 5.7; MRG = − 4.98 to − 5.96) but the VMG is slightly enriched in 87Sr/86i = 0.7087–0.7098 as well as in δ18O in the range of 10.6‰ to 11.0‰ than the MRG with 87Sr/86i = 0.7064–0.7075 and δ18O = 9.9‰–10.5‰. These granites are associated with coeval scarce grabroic intrusions and/or mafic microgranular enclaves which are not considered as mafic precursors of the associated granitic magmatism. Instead, a lower metaigneous crustal source, at different levels, is proposed based on the available data set.