Modeling the role of erosion in diapir development in contractional settings

The Cardona diapir of Eocene salt (Cardona salt formation) crops out in the deformed foreland of the Pyrenees. The diapir pierces 300 m of sediments on the northern limb of the northeast-southwest trending Cardona-Pinós fold close to the hinge area, and is 2 km long and 0.7 km wide at the surface. Dynamically scaled models were laterally shortened in a centrifuge in order to investigate the mechanism that triggered the Cardona diapir, and the role of postshortening erosion in its development. The models consisted of a microlaminate overburden simulating nonevaporitic sediments overlying a layer of silicone putty simulating rock salt. Model results show that moderate folding of overburden units causes the underlying ductile layer to flow from under syncline troughs to accumulate in the anticline cores. Postshortening erosion of one of the models thinned and weakened the overburden above the salt-cored anticlines and aided piercement of salt walls along the crests of the anticlines. Our models show that anticlines need to be open structures in order to allow accumulation of sufficient salt to rise diapirically when the overburden is thinned by erosion. Minimum ascent velocities, which were calculated using the deformed Pliocene-Pleistocene deposits around the Cardona diapir, support a postshortening age for salt piercement after 2.2 km of overburden was eroded from the crest of the anticline 2 Ma ago.