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

Abstract

The Variscan Belt in western Europe shows an arcuate geometry that is usually named Ibero-Armorican Arc. The nucleus of this arc, known as the Asturian Arc, comprises the Cantabrian Zone which is a foreland fold and thrust belt. The Trubia River area is located in the inflexion zone of the Asturian Arc, which is a strategic structural position for unraveling the geometry and kinematics of the Variscan thrust sheets and related folds. Geological mapping, construction of stratigraphic and structural cross sections, analysis of kinematic indicators, and estimate of shortening for each cross section 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 have been interpreted as fault-propagation folds. The emplacement directions measured in the Trubia River area change from north to south and converge towards the core of the Asturian Arc. The minimum shortening estimated ranges between 16.4 and 17.6 km, which corresponds to 56.9 and 59.4%. The complex crosscutting relationships between folds and thrusts suggest that, in general, the different structural units followed a forward-breaking sequence of emplacement, with some breaching and a few out-of-sequence thrusts.

Foreland- and hinterland-verging structures in fold-and-thrust belt: an example from the Variscan foreland of Sardinia

“…Compared to the Variscan foreland in S-Sardinia, many features are similar: very low or non-metamorphic condition, the same deformation age (Early Carboniferous), lack of important magmatism and a polyphase structural history (Julivert 1987). Bulnes and Aller (2002) and Bulnes and Marcos (2001) highlights the close linkage between thrusts and folds, interpreted as fault-propagation folds deforming older thrusts and folds during progressive thrust imbrications and folding towards the foreland. An important difference is that in the Cantabrian Zone a significant change in tectonic transport direction is not described, and the finite deformational architecture is quite different, without the formation of triangle zone.…”

Folding in orogens: a case study in the northern Iberian Variscan Belt

“…Nevertheless, there are also longitudinal folds that were formed to balance totally or partially the displacement of thrusts (Alonso, 1987). Among them, fault-propagation folds are common in the north-western sector of the Cantabrian zone (Alonso et al, 1991;Alonso and Marcos, 1992;Bulnes and Marcos, 2001;Bulnes and Aller, 2002), and folds detached on footwall flats or folds associated with hanging-wall ramps have been described in the southern part of the Cantabrian zone (Alonso, 1987).…”