New insights from an emplacement model for the Santa Eulalia Plutonic Complex (SW Iberian Peninsula)

The Santa Eulalia Plutonic Complex is formed by two main granites: G0 and G1. The G0 granite hosts metasedimentary carbonate and pelitic rocks (roof pendants) and elongated masses of mafic-intermediate rocks (the M-group). The host rocks form a diverse 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-Cordoba sinistral shear zone) and is cut by the Alter do Chao and Assumar faults. The geological complexity of the area makes it difficult to determine the emplacement mechanism of the pluton. We propose a model for the ascent and emplacement of the pluton that can also be applied to similar post-collision Variscan granites. The gravity anomalies suggest that the pluton is slightly asymmetrical and extends to the SSE beneath the host rocks; its main root is >8 km thick in its deepest areas. The available radiometric data for an extended area embracing several regional plutons suggest a west-east magmatic alignment. The Variscan structures probably formed efficient crustal discontinuities enabling the generation and ascent of magma. Our model involves a west-east magmatic axis for magma spreading along extensional fractures (T-fractures) related to the Tomar-Badajoz-Cordoba 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 represented well by outcrops of porphyritic biotite granites (the Ervedal, Fronteira and G1 granites).

Automated summary

The Santa Eulalia Plutonic Complex consists of two main granites, G0 and G1. The geological complexity of the area, along with Variscan structures and faults, makes it challenging to determine the emplacement mechanism of the pluton. However, a proposed model suggests a west-east magmatic axis and the involvement of extensional fractures in the ascent and emplacement of the plutonic rocks.