PETROLOGY AND GEOCHEMISTRY OF THE FELSIC HYPABYSSAL MAGMATISM IN NORTHERN PORTUGAL (CENTRAL IBERIAN ZONE)

Abstract

In the Central Iberian Zone, multiple subvolcanic intrusions were emplaced during the final stages of the Variscan orogeny. The felsic component of this magmatic episode is mainly represented by dykes and masses of granite porphyries and microgranites, which can be commonly found in northern Portugal. Overall, these rocks are more evolved and enriched in rare incompatible metal elements (such as Li, Be, Rb, Cs, Nb, Ta, Sn, and W) when compared to the regional Variscan granites. The data acquired from the lithogeochemical study reported in this paper suggest that most porphyries/microgranites presumably resulted from anatexis of metapelitic protoliths, with some metagreywacke/orthogneiss contribution. The existing compositional diversity is essentially explained by important differences regarding partial melting conditions, source heterogeneity, and the crystal fractionation phenomenon. The aforementioned enrichments are most likely associated with the composition of the sources, muscovite and biotite-dehydration-melting reactions, and fractionation of feldspar, biotite, and Fe-Ti oxide-dominated mineral assemblages.