The formation of an orocline by multiphase deformation: a paleomagnetic investigation of the Cantabria–Asturias Arc (northern Spain)

The Variscan orogeny in the Cantabria–Asturias Arc (CAA) of northern Spain represents a multiphase deformation history associated with Pangea’s amalgamation. To determine the timing and kinematic history of deformation, a paleomagnetic investigation was carried out on Devonian limestones in three structural domains of the CAA’s hinge zone. aracteristic remagnetizations in the CAA are distinguished: an Early Permian (B) component that postdates initial Westphalian–Stephanian aged folding (F1 and F2), and a Late Carboniferous (C) component that postdates F1 deformation. Both the B and C magnetizations experienced a later F3 folding phase. The kinematics and geometry of post-magnetization deformation are determined by bringing measured magnetic directions into agreement with reference directions. These structural corrections also allow separation of deformation events in time. We conclude that generally east–west-trending, but variably plunging, fold axes characterize F3 folding in the hinge zone of the CAA. This post-magnetization deformation involved significant amounts of tilting and (sub)vertical axis rotation, which together produced clockwise rotation in the north of the arc and counterclockwise rotation in the south of the arc, to form the horseshoe-shaped orocline that is observed today. F3 fold axes change from near-vertical to moderately inclined between and within structural domains, due to the structural fabric imposed by F1 and F2. Based on calculated F3 fold properties, we can reconstruct pre-existing F1 and F2 structural geometries of the hinge zones. This analysis shows that F1 and F2 structures are the result of Late Carboniferous deformation, as part of the same east–west but temporally discrete compression regimes. On the other hand, F3 is controlled by Permian, north–south compression (in present-day coordinates).