Variscan Orogeny
Abstract
The Variscan (often termed Hercynian) orogeny spans most of central and south-eastern Europe from South Portugal to Poland and beyond into the Balkans and Turkey. It is a collage of microcontinents which drifted off from the northern margin of Gondwana and includes Avalonia and the Armorican Terranes Assemblage (ATA). Break-up started by southward subduction under Gondwana during the Late Neoproterozoic to Early Cambrian. Back-arc extensional belts evolved into Middle Cambrian to Devonian rift/drift zones separating the microcontinents from each other and from Gondwana. Those microcontinents were caught up in the later Paleozoic collision between Gondwana and Laurussia. Closure of the intervening oceans occurred between the mid-Devonian and the early Carboniferous and (as seen in central Europe) proceeded from south to north. Collision continued into the latest Carboniferous and was accompanied by dextral transpressional shear zones and oroclinal bending. Plate convergence resulted in a bilateral symmetry. The existence and correlation of median massifs between the opposed flanks of the Variscides are controversial, as is the lateral continuity of metamorphic rocks representing the infill and basement of the Galicia-Moldanubian Ocean between the ATA and the Gondwana mainland. The paleogeographic affiliation of the Moroccan Meseta (now adjacent to South Portugal) is uncertain, although the Anti-Atlas and Variscan fragments framing the Gibraltar Arc clearly belong to the north-Gondwana mainland.