Características y significado del volcanismo ordovícico-silúrico de la serie autóctona envolvente del Macizo de Cabo Ortegal (Galicia, NW España)

Abstract

Metavolcanic levels with acid to intermediate composition are wide-spread in the ordovician-silurian autochthonous sequence croping out below the Cabo Ortegal allochthonous Complex. Generally, they are blastoporphyritic metavolcanic rocks with medium to coarse size phenocrysts. They are concordant or subconcordant levels, overtaking 150 meters in width, interbedded in greenschist facies metasediments. Compositionally they are high-K calc-alkaline and shoshonitic rocks, and the dacites and rhyolites terms are the commonest in both series. In some places, the metavolcanic rocks include autoliths of biotite tonalites and biotite microsyenites. The latest lithology may appear forming a stratoidic body, about 30 meters width, in relation with the greatest size metavolcanic level. According to the textures of the rocks, we can recognize extrusives and domatic types. The later are coarse grain rocks and they are generally intrusives into the effusive types. The characteristics of the volcanism are compatible with subaerial extrusions, taking place during a continental rifting process affecting the NW of the Iberian Península during Ordovician and Silurian time.