A cross-section through the northern part of the Iberian Massif

Abstract

The Iberian Massif forms the western extremity of the Variscan Fold Belt in Europe, which from the Armorican Massif describes a sharp bend (the lbero-Armorican arc) to cross the Iberian Peninsula from northwest to southeast. A cross-section through the massif shows the existence in the belt of two branches with an opposite polarity, which gives a certain mirror-image symmetry to the structure of the belt. An east-west section parallel to the Cantabrian coast provides the best cross-section of the northern branch of the Iberian Massif. This section shows the typical zonation of linear fold belts. It consists of an 'external' part (Cantabrian zone) formed by carbonaceous and terrigenous rocks in a varied platform facies (at least the pre-Carboniferous rocks) and with thin-skinned tectonics, and an 'internal' part with a more monotonous, pelitic facies, and in general with cleavage, metamorphism and plutonism. The facing of the main structures is towards the 'external' part of the belt. During pre-Carboniferous Palaeozoic time, the geological evolution can be explained as the result of tension resulting in normal faulting, synsedimentary volcanism and intrusion of peralkaline and calcalkaline granitoids. The source of terrigenous supply was near the core of the arc, where an uplift tendency existed. Coinciding with the Devonian-Carboniferous boundary there was a break in the geological history and the subsequent geological evolution has been controlled by compressional orogenic events. This break is shown by a change in terrigenous supply now derived from the rising chain, by the development of foredeeps in the frontal part of the chain, and by the change from anorogenic to orogenic conditions with folding, metamorphism and plutonic intrusion.