Insights for late-Variscan kinematics and oroclinal bending in the Central Iberian Zone from the paleomagnetic characterization of the Cambrian Urda-Los Navalucillos Limestone (Montes de Toledo, Spain).

As a result of the collision of Gondwana, peri-Gondwanan terranes, and Laurussia in the Upper Devonian to early Permian, various Paleozoic oceans are thought to have closed, leading to the formation of the Variscan belt. The belt experienced oroclinal bending in the latter phases of the orogeny, a process that became significant in the Iberian Massif, the westernmost part of the European Variscan belt. There, the belt acquired an S-shaped attitude defined by the Central Iberian Arc (CIA) to the south and the Ibero-Armorican Arc (IAA) to the north. The early Variscan structures, the magnetic anomalies, and the tectonostratigraphic zonation of the Iberian Massif are all bent by both arcs.

The IAA is extensively studied, but the tectonic evolution of the CIA is not well resolved because a large part of it is covered by sediments of the Paleogene Duero basin. Paleomagnetism is a very useful tool used to identify possible vertical axis rotations. Therefore, we carefully searched for outcrops that may record paleomagnetic directions that could shed some light on the development of the CIA.

Weakly metamorphic Cambrian limestones from the southern limb of the CIA were subjected to magnetic and paleomagnetic investigations. 32 sites in 5 outcropping structures in the Urda-Los Navalucillos Formation of Montes de Toledo (Central Iberian Zone, Spain), close to the CIA hinge zone, yielded more than 270 cores. These outcrops were affected by two regional-scale Variscan folding phases, namely C1 and C3, which developed interference patterns. A characteristic paleomagnetic component was found at 19 sites in 4 of the structures. This component reveals different temporal correlations with C3 folds, from syn-folding to certainly post-folding. The resulting mean directions of the magnetic vector, in geographic coordinates, consistently display northward to north-western declinations and negative, low inclinations, indicating that they have been acquired before the geomagnetic reverse polarity Kiaman superchron when Iberia was in the southern hemisphere. Although the inclination of the paleomagnetic mean directions is consistent amongst structures, the declination varies from N to NW, suggesting a vertical axis rotation synkinematic to C3 folding previous to 318 Ma. These directions indicate that the early evolution of the southern limb of the CIA was differentially recorded by the paleomagnetic directions of the different structures and underwent a 42º clockwise rotation during the late Carboniferous. The later development of the IAA was associated with a significant counterclockwise rotation that affected the entire paleomagnetic record. (Research support: SA084P20, PID2020-117332GB-C21, PID2019-108753GB-C21, AEI/10.13039/501100011033, FPU16/00980, PTA2017-14779-I and FJC2019-041058-I)