Petrogénesis del plutón de Santa Eulalia (Alto Alentejo, Portugal)

Abstract

The Santa Eulalia batholith (Alto Alentejo, Portugal) is a plutonic complex of late Variscan age located in the Northern part of the Ossa-Morena Zone. This pluton is made up of granites grouped in two facies: (i) the external granite, formed by granites showing equigranular texture, dominant K-feldspar and biotite as the main mafic mineral, (ii) the central granite, has equigranular texture and a biotite ± muscovite asociation. Several gabbro-diorite and granodioritetonalite igneous bodies also occur. The external granite shows a ring-type outcrop pattern, and includes most of the gabbro-diorite and tonalite-granodiorite rocks as well as large metasedimentary country rocks. The central granite forms a circular outcrop and is totally surrounded by the external granite. The data available suggest that all of the igneous units forming this batholith are coeval although petrogenetically independent. We propose that the gabbrodiorite rocks derive from an enriched mantle source. These rocks show no or little crustal contamination. Partial melting in the low-middle crust of mafic/gneissic lithologies and intermediate igneous/metasedimentary lithologies generated the tonalite-granodiorite rocks and the granite rocks of the pluton respectively. The emplacement in the upper crust probably started with the gabbro-diorite and tonalite-granodiorite igneous magmas, being followed almost simultaneously by the external granite. The central granite might have intruded shortly after the extenal granite, pushing aside all of the previous units and thus generating the annular outcrop pattern.