Influence on preexisting salt diapirs during thrust wedge evolution and secondary welding: insights from analogue modeling

Abstract

Salt lithologies are mechanically weaker than other sedimentary rocks. Salt horizons usually act as décollements and precursor salt bodies preferentially deform early during contraction, concentrate deformation, and impact the structural style and kinematics during mountain building. Focusing on shortened isolated-diapir provinces, our analog modeling program investigates the influence of two salt walls on folding and thrusting. High resolution topographic scans and particle image analysis show that the presence of precursor diapirs impacts the layer parallel shortening patterns and presumably the stress field at the onset of contraction. Shortening concentrates on diapirs, leading to roof arching, crestal extension and salt extrusion. This sequence of events occurs earlier on thinner salt- sediment sequences including diapirs having well-developed pedestals, particularly when proximal to the deformation front. Folds and thrusts nucleate at salt walls if they feature a well-developed pedestal. Further shortening results in secondary welding as evidenced by the collapse of uplifted roof domes, cessation of indentation and reverse faulting nucleated at the secondary welds. Meanwhile, and depending upon the processes occurring on the diapir closer to the backstop, the deformation of the distal salt wall is discontinuous. Our modeling results are compared with experimental works and natural examples from the Fars (Zagros Mountains).