One or two oroclines in the Variscan orogen of Iberia? Implications for Pangea amalgamation

Abstract

The supercontinent Pangea formed in the late Carboniferous as a result of the Gondwana- Laurussia collision, producing the strongly sinuous Variscan-Alleghanian orogen. Iberia is interpreted to comprise two Variscan bends, forming an S-shaped orogenic belt: the Cantabrian orocline to the north and the Central Iberian bend to the south. Coeval formation of both oroclines, however, requires significant north-south shortening (in present-day coordinates) during Pangea's amalgamation. In contrast to the Cantabrian orocline, neither the kinematics nor geometry of the Central Iberian bend is well constrained. We provide paleomagnetic data from the southern limb of the Central Iberian bend, showing ~60° counterclockwise vertical axis rotation during the late Carboniferous to early Permian, comparable to that determined for the southern limb of the Cantabrian orocline. This result is incompatible with the hypothesized S-shaped bend in the Iberian Variscides. We argue that Central Iberia, if really bent, must have acquired its curvature before the Cantabrian orocline, the curvature being an inherited structure. We propose a new mechanism of Pangea formation, compatible with the geology, geochronology, and paleomagnetism, in which a clockwise rotation of Gondwana produces the necessary change in the stress field to form the late Variscan Cantabrian orocline.