The fracture pattern of the Sant Corneli Bَixols oblique inversion anticline (Spanish Pyrenees)

In this work we present and discuss the macro and mesostructural deformation patterns of the Late Cretaceous Sant Corneli Bóixols oblique inversion anticline (Spanish Pyrenees). This E–W striking and south-verging structure developed by inversion of an Early Cretaceous extensional fault system, formed by WNW–ESE striking faults (oriented perpendicular to the Early Cretaceous stretching direction) and transfer faults. During inversion, the shortening direction was oriented NNW–SSE, i.e. oblique to both basin margin and inherited extensional deformation structures. A pre to early-folding layer-parallel shortening (LPS) stage caused the strike-slip reworking of inherited extensional structures and the development of extensional and contractional structures oriented parallel and perpendicular to the shortening direction, respectively. Few faults clearly developed during the late stages of fold growth, in response to a stress field having principal axes parallel to those of the layer-parallel shortening event, i.e. oblique to the fold axis. WSW–ENE striking bedding-perpendicular joints and veins postdate the LPS pattern and can be associated with a syn-folding layer-parallel stretching. Analogously, few reverse faults having a top-to-the crest shear sense are associated with flexural-slip folding. Both layer-parallel stretching and shear sense provided by flexural-slip related elements are not perpendicular to the fold axial trend. All these assemblages were overprinted by a set of post-folding extensional structures oriented oblique to the strike of the anticline. ted data show that syn-inversion fractures in the Sant Corneli Bóixols Anticline are neither parallel nor perpendicular to the fold axial trend, and their development has been controlled by inherited extensional structures and the regional shortening direction.