Origin of the western Subbetic arc (South Spain): palaeomagnetic and structural evidence

Abstract

An integrated structural and palaeomagnetic study in Late Cretaceous—Eocene rocks of the western Subbetic arc in the Betic Cordillera of southern Spain shows that the change in fold trend around the arc is significantly greater than the variation in primary magnetic declination. This suggests that the arcuate geometry is not primarily a consequence of differential rotation. The area has experienced a regional clockwise rotation of at least 40 °, which was most probably imposed during oblique WNW-directed convergence along the southern Iberian margin in early Miocene time, before the arcuate structure was formed. Kinematic indicators associated with the arcuate folds and thrust traces arc for the most part consistently WNW-directed. suggesting that the arc is not primarily a result of variations in the direction of tectonic transport. The arcuate structure was probably initiated without significant rotation by the WNW-directed indentation of the curved western end of the Alboran domain into the Iberian margin, and was then tightened, involving up to about 35 ° of further rotation in different segments of the arc. Finally, one sector in the arc was rotated anticlockwise by about 40 ° with respect to the rest of the region, reorientating the magnetic declinations, the fold trends, and the kinematic indicators. This rotation was associated with local sinistral shear.