Geology of the Cabuerniga Fault System: evolution of a large Alpine structure with Variscan inheritance

The Cabuerniga Fault System (CFS) extends for 150 km in E-W trend along the northern divide of the Cantabrian Mountains, near the Cantabrian Sea. This fault system was reactivated several times since the Paleozoic, and displays hydrothermal activity nowadays. We present here a detailed geological map of the whole CFS and six cross-sections distributed along strike, which allowed us to unravel the kinematic history of the individual fault segments comprising the CFS. The current CFS geometry mainly results from the reactivation of E-W Variscan thrusts and NW-SE Late-Variscan strike-slip faults during the Alpine Cycle. Reactivation took place in relation to both Permian and Mesozoic pre-orogenic extension and subsequent Cenozoic shortening. The eastern end of the CFS corresponds to a N-S structure arriving at the Cantabrian coast, while the western edge connects with the E-W trending Llanera fault, leading to an Alpine fault system extending 220 km.