THE CENTRAL IBERIAN ARC (VARISCAN BELT)

An arcuate structure, comparable in size and tightness to the well-known Iberian-Armorican arc, is delineated by magnetic anomalies and Variscan fold traces in the Central Iberian Zone of the Iberian Massif, as can be seen in the aeromagnetic and geological maps of Spain (Ardizone et al., 1989; ITGE, 1995). The structure seems to have remained unnoticed due to the faintness of the anomalies and the Meso- and Cenozoic deposits covering the hinge zone of the arc.

The sense of curvature of the new orocline, tentatively named the Central Iberian arc, is opposite to that of the Iberian-Armorican arc. Its core is occupied by the allochthonous complexes of NW Iberia, which include the Rheic suture, and the part of the Central Iberian Zone to the ESE of the Morais Complex. The Ossa-Morena Zone does not appear involved.

The arc explains the large width of the Central Iberian zone (up to 400 km) by duplication of a strip initially half that width. It makes more understandable the position of the allochthonous complexes of NW Iberia, and opens new perspectives for correlations with the rest of the Variscan belt, in particular, with the Armorican Massif, whose central domain could be the continuation of the southern branch of the arc detached by strike-slip tectonics.

The opposite curvature of the Central Iberian and Iberian-Armorican arcs might suggest a common origin as a pair of asymmetric folds related to plate-scale wrench tectonics of left-lateral movement according to the "S" pattern drawn by both arcs. However, both limbs of the Central-Iberian arc are dragged by the right-lateral Porto-Tomar fault which, in turn, seems bent by the Iberian-Armorican arc in its continuation to the South Armorican shear zones. Confirmation of these crosscutting relationships would indicate a previous development of the Central Iberian arc, as well as a possible relationship with a right-lateral fault at its southern limit.

REFERENCES

Ardizone, J., Mezcua, J., and Socías, I. 1989. Mapa aeromagnético de España Peninsular 1:1000000. Instituto Geográfico Nacional, Madrid.

ITGE. 1995. Mapa Geológico de la Península Ibérica, Baleares y Canarias 1:1000000. Instituto Tecnológico GeoMinero de España, Madrid.