Paleomagnetism in the Cambrian Urda-Los Navalucillos Limestone (Montes de Toledo, Spain): Implications for late-Variscan kinematics and oroclinal bending in the Central Iberian Zone

Abstract

A magnetic and paleomagnetic study was carried out on weakly metamorphic Cambrian limestones from the southern limb of the Central Iberian Arc (CIA), a late-Variscan orocline located to the south of the Ibero-Armorican Arc (IAA). >270 cores were obtained from 32 sites located at 5 outcropping structures in the Urda-Los Navalucillos Formation of Montes de Toledo (Central Iberian Zone, Spain), in an area close to the hinge zone of the CIA. These outcrops are affected by two regional-scale Variscan folding phases, namely C1 and C3, which developed interference patterns. A characteristic paleomagnetic component was isolated in 19 sites at 4 of the structures, which shows different temporal relationships with C3 folds, ranging from possibly syn-folding to clearly post-folding. The resulting mean directions of the magnetic vector, in geographic coordinates, always show northward to north-western declinations and negative, low inclinations, suggesting acquisition during some normal polarity event(s) when Iberia was located in the southern hemisphere, i.e. prior to the geomagnetic reverse polarity Kiaman superchron. While the inclination of the paleomagnetic mean directions is coherent between structures, the declination ranges from N to NW, suggesting a vertical axis rotation synkinematic to C3 folding, and older than 318 Ma. These directions suggest that the southern limb of the CIA first underwent a 42° clockwise rotation during the late Carboniferous that can be related to the development of the CIA, and which has been differentially recorded by the paleomagnetic directions of the different structures. This was later followed by a large counterclockwise rotation related to the formation of the IAA, which affects to the entire paleomagnetic dataset.