Passive-roof thrusting in the Messinian Vena del Gesso Basin (Northern Apennines, Italy): constraints from field data and analogue models

We present the results of a study of the Vena del Gesso Basin (Romagna Apennines, Italy) integrating field analyses and analogue modelling. This basin represents one of the best-preserved top-thrust basins in the Northern Apennines foreland and is one of the few examples where primary evaporites, related to the Messinian salinity crisis of the Mediterranean, widely crop out. The structural style affecting the Messinian gypsum is examined to get insights into the mechanism responsible for the overall deformation features recognizable in the area. The evaporites are completely detached at the base and widespread back-thrusts, repeatedly doubling these deposits, strongly contrast with the regional forelandward vergence of structures in the Apennines. On the basis of the comparison between field data and experimental results, the features characterising this area can be described as the result of the deformation linked to the sequential activation of an obliquely propagating passive-roof duplex. Analogue models evidenced the major role played (1) by syntectonic erosion that promoted the development of passive-roof duplex style, as well as (2) the role of décollement level pinch-out that determined an oblique progression of deformation. Finally our data lead to reconsider the palaeoenvironmental reconstruction concerning the onset of the Messinian salinity crisis in the Mediterranean.