Quaternary deformation and stress perturbations along the Digne thrust front, Southwestern Alps

Abstract

In the southwestern Alps, the retrogradation of the continental sedimentary wedge that infilled the Valensole foreland basin after the Messinian event, resulted in the deposition of recent (3.4 to 2 Ma) and thick (up to 100m) conglomerates within canyons in the Digne thrust sheet. Paleostress analysis, in these Upper Pliocene-Quaternary sediments and in a Quaternary terrace, allows characterizing the local Quaternary stress field. This stress field displays typical stress perturbations (deviation of σ1 of up to 53°) along a main dextral fault (Bès fault, 0.7mm/yr) of the strike-slip edge of the Digne south-verging thrust sheet. We propose a structural model that explains the highest tectonic uplift recorded by the paleo-drainage network (345m; 0.1mm/yr) at the northern tip of this dextral fault. We conclude that Messinian-Zanclean canyons allow one to characterize Quaternary geodynamics for deformation rates as low as 0.1mm/yr.