Internal structure of a detachment horizon in the most external part of the Pyrenean fold and thrust belt (northern Spain)

Abstract

Abstract The thick Eocene Cardona salt forms the detachment horizon of the most external part of the Pyrenean fold and thrust belt. This salt horizon forms the cores of anticlines and is intensively mined for potash. The study of the structure of the salt layer at three sites (Cabanasses, Súria-Shaft IV and Balsareny underground mines) reveals that the metric and decametric scale structures are consistent with deformation in a shear zone (detachment horizon) with a shear sense of top-to-the-south and not related to compressional or diapiric folding. A further study shows that these structures are later modified by larger wavelength folds and thrusts which have a surface expression. The total horizontal shortening in the two anticlines studied (Súria and El Guix) is a minimum of 750 m. All the folds developed in the detachment horizon have horizontal axes which are normal to the shear direction. This contrasts with folds developed in detachment horizons with intense shearing, where folds with axes parallel to shear direction are common.