Along-strike extrusion at the transition between thin- and thick-skinned domains in the Pyrenean Orogen (northern Spain)

Abstract

AbstractIn the south-verging portion of the western Pyrenean Orogen, a Mesozoic basin and part of the adjacent continental margin were deformed during the Pyrenean collisional stage. The slight obliquity between extensional and compressional trends, and the presence of a Mesozoic Transfer Zone, implied that both extensional domains were exposed along-strike of the belt in the same structural position. These two areas are not only characterized by the widespread reactivation of inherited fault systems but also by different styles of deformation related to the presence or absence of an evaporitic detachment level. To the east, in the Mesozoic basin, a large-displacement south-directed low-dipping thrust detached above Triassic evaporites is present. To the west, in the Mesozoic continental margin, thick-skinned and deeply rooted right-lateral and reverse faults become first-order elements. The presence of a strike-slip component produced the eastwards extrusion of the eastern portion of the Mesozoic continental margin, which imposed an along-strike shortening at the edge of the extruded block. The transitional area from thin- to thick-skinned style of deformation, from a dip-slip to a transpressive framework, and the area accommodating the extrusion are located along a north–south-orientated band representing the southern extension of a Mesozoic Transfer Zone.