The Kinematics of a salt sheet recorded in an array of discorted intrasalt stringers (Les Avellanes Diapir - Sputh-Central Pyrenees)

Abstract

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