New insights for an emplacement model for the Santa Eulália Plutonic Complex (SW of Iberian Peninsula)

Abstract

The Santa Eulália Plutonic Complex is formed by two main granites, G0 and G1 granites. Within the G0 granite there are metasedimentary carbonate and pelitic rocks (roof pendants) and elongated masses of mafic-intermediate rocks (M-group). The host rocks comprise a diversified sequence of igneous, metasedimentary and metamorphic rocks. The study area is constrained by Variscan structures formed in a transpressional/transtensional sinistral tectonic regime – the Tomar-Badajoz-Córdoba sinistral shear zone, and is cut by the Alter do Chão and Assumar faults. The geological complexity of the area makes hard to determine the emplacement mechanism of the pluton. Herein, a model is proposed for the ascent and emplacement of the pluton; this model can also be applied to similar post-collision Variscan granites. The gravity anomalies suggest that the pluton is slightly asymmetric and extends to the south-southeast beneath the host rocks, and its main root has a thicknesses of more than 8 km in its deepest areas. Complementarly, the available radiometric data for an extended area embracing several regional plutons suggest a W-E magmatic alignment. The Variscan structures likely constituted efficient crustal discontinuities enabling the generation and ascent of magma. Our model involves a W-E magmatic axis for magma spreading along extensional fractures (T-fractures) related to the Tomar-Badajoz-Córdoba shear zone. The opening movement along these fractures, created divergent forces that allowed the ascent and emplacement of the plutonic rocks. The importance of these fractures is well represented by the outcrops of the porphyritic biotite granites (Ervedal, Fronteira and G1 granites).