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 sync line in the western hinge zone of the Variscan foreland fold and thrus t belt of northern Spain was carried out to constrain the tectonic def ormation of the Cantabrian Are. Results show a complex pattern of stru ctural deformation and acquisition of at least two secondary syntecton ic magnetizations, On the basis of local and regional fold tests we do cument an Early Permian (B) component that postdates earlier (F1) West phalian 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 m agnetite, The C component is carried by magnetite in the gray carbonat es and by hematite in the red beds, Both B and C components reveal sig nificant vertical-axis rotations that indicate that an originally cyli ndrical Lagos del Valle Syncline was refolded (F2) about a vertical ax is after acquisition of the B component magnetization, The pattern of rotations suggests that the entire Cantabrian Are may have originated as a much more linear fold and thrust belt, which was later modified b y significant oroclinal bending with relative rotations totaling at le ast 120 degrees. The temporal distribution of remagnetization and defo rmation also suggests a protracted Variscan orogeny in the area, lasti ng from at least the Late Carboniferous into the Permian.