Internal structure and kinematics of Variscan thrust sheets in the valley of the Trubia River (Cantabrian Zone, NW Spain): regional tectonic implications

The Variscan Belt in western Europe shows an arcuate geometry that is usual ly named Ibero-Armorican Arc. The nucleus of this are, known as the Asturia n Arc, comprises the Cantabrian Zone which is a foreland fold and thrust be lt. The Trubia River area is located in the inflexion zone of the Asturian Arc, which is a strategic structural position for unraveling the geometry a nd kinematics of the Variscan thrust sheets and related folds. Geological m apping, construction of stratigraphic and structural cross sections, analys is of kinematic indicators, and estimate of shortening for each cross secti on have been carried out. This area consists of two major antiform-synform pairs related to two imbricate thrust systems. These folds are asymmetric, tight, and their axial traces follow the trend of the Asturian Arc. They ha ve been interpreted as fault-propagation folds. The emplacement directions measured in the Trubia River area change from north to south and converge t owards the core of the Asturian Arc. The minimum shortening estimated range s between 16.4 and 17.6 km, which corresponds to 56.9 and 59.4%. The comple x crosscutting relationships between folds and thrusts suggest that, in gen eral, the different structural units followed a forward-breaking sequence o f emplacement, with some breaching and a few out-of-sequence thrusts. The a nalysis of the transport vectors together with the disposition of the fold axes and post-thrusting faults that deform the thrust stack are evidence of a late deformation event that is partially or totally responsible for the arcuate form of the Asturian Arc. The timing of the Asturian Arc, amount of shortening, and sequence of emplacement of the structures are in accordanc e with previous regional studies of the Cantabrian Zone.