The kinematics of a salt sheet recorded in an array of distorted intrasalt stringers (Les Avellanes Diapir - South-Central Pyrenees)

Stringers represent fragments of competent, brittle layers, formerly interstratified within a layered evaporite sequence (LES) that are entrained and deformed by viscous flow. To resolve the impact of the stringers on the deformation style of an extrusive salt sheet, an array of decameter-thick, carbonate stringers, preserved in the caprock matrix of the Les Avellanes Diapir (South-Central Pyrenees) was analysed. The diapir exposure was mapped in detail to produce a cross-section that shows the stringer assemblage. To understand the dynamic behaviour of stringers, this natural prototype has been reproduced using scaled analogue models. In the model, stringers were carried into the salt sheet, rotating and deforming while migrating toward the sheet front. The array of stringers can be divided into the following three structural domains: 1) a feeder domain mainly hosting vertical stringers parallel to the stem wall that rotate to a subhorizontal orientation as they approach the allochthonous sheet, 2) a sheet domain containing stack-like sets of subvertical and overturned, to subhorizontal stringers, as well as isoclinally and recumbently folded stringers, and 3) a sheet front domain characterised by stringers dipping toward the salt sheet front. Compartmentalization of the horizontal flow by the transported stringers controlled the deformation in the caprock matrix above. Finally, the similarity between the field observations and the model is evaluated and discussed to shed light on the Les Avellanes Diapir kinematic evolution.