From thrust tectonics to diapirism. The role of evaporites in the kinematic evolution of the eastern South Pyrenean front

Abstract

The South Pyrenean foreland has a buried thrust front geometry where evaporitic levels are present at the subsurface and are suitable to be detachment horizons. The thrust wedge geometry developed at the externalmost limit of the evaporitic levels permits to define the South Pyrenean Triangle zone. This triangle zone is an excellent scenario to study the influence of evaporitic layers in the thrust front geometry of a fold and thrust system and in the development of thrust wedges. Analogue modelling shows different thrust wedge geometries through the deformation history in relation to the different rheological properties of the detachment horizons. Presence of strain markers in the field permited to quantify strain in the overburden. In addition, the possibility to access to the detachment at different locations permitted the comparison between the deformation in the overburden and in the detachment horizon from the most frontal structures to the hinter ones. The structure in the detachment horizons are well preserved because the evaporitic levels are layered and because bulk shortening is small. Finally, analogue modelling of the development of a diapir near the crest of an anticline suggested a new hypothesis of the formation of diapirs in areas that have undergone compression.