The influence of the geometry of salt detachments on thrust salient development: An analogue modelling approach based on the South-Central Pyrenean thrust salient

Abstract

Inspired by the structural evolution of the South-Central Pyrenean Thrust Salient we have designed an experimental program to investigate the role of the geometry of viscous detachments on the formation of thrust salients. The precontractional wedge geometry of the salt overburden facilitates propagation of the deformation front to the forward edge of the viscous detachment. As deformation progresses, interaction between structures formed above the viscous detachment and the adjacent frictional detachment mostly depends on the angles of the lateral edges of the weak layer with respect to the shortening direction. The orientation of the oblique structures defining thrust salients does not generally mimic the edges of the viscous detachment. They can even form at a high angle to the shortening direction if active structures in the frictional and viscous detachments connect along-strike. Thrust wedges above frictional and viscous detachments show different kinematic evolution. During the late stages of deformation frictional wedges propagate forward whereas viscous wedges deform internally by break-back thrust sequences. Both wedges show along-strike differences of the surface taper that have an impact on the evolution of the topography and related synorogenic sediment dispersal. Experimental results are consistent with the structural evolution and tectono-sedimentary relationships observed in the South-Central Pyrenees.