Kinematic constraints on thrust‐belt curvature from syndeformational magnetizations in the Lagos del Valle Syncline in the Cantabrian Arc, Spain

A detailed paleomagnetic study in a single, first‐order, refolded syncline in the western hinge zone of the Variscan foreland fold and thrust belt of northern Spain was carried out to constrain the tectonic deformation of the Cantabrian Arc. Results show a complex pattern of structural deformation and acquisition of at least two secondary syntectonic magnetizations. On the basis of local and regional fold tests we document an Early Permian (B) component that postdates earlier (F1) Westphalian and Stephanian thrusting and folding and a Late Carboniferous to earliest Permian (C) component that is synfolding, acquired during Fl. The B component only resides in the carbonates and is carried by magnetite. The C component is carried by magnetite in the gray carbonates and by hematite in the red beds. Both B and C components reveal significant vertical‐axis rotations that indicate that an originally cylindrical Lagos del Valle Syncline was refolded (F2) about a vertical axis after acquisition of the B component magnetization. The pattern of rotations suggests that the entire Cantabrian Arc may have originated as a much more linear fold and thrust belt, which was later modified by significant oroclinal bending with relative rotations totaling at least 120°. The temporal distribution of remagnetization and deformation also suggests a protracted Variscan orogeny in the area, lasting from at least the Late Carboniferous into the Permian.