Relief distribution, morphology and Cenozoic differential uplift in the Argentera Massif (French-Italian Alps)

Relief analyses were carried out in the south-eastern part of the crystalline Argentera Massif, using the classical geomorphometric parameters (local relief, depth of incision and fraction of the relief occupied by valleys). The aim of this analysis is the morphological characterisation of the opposite slopes of the axial chain and the explanation of orographic problems in this sector of the Alpine chain. The relief analysis, carried out with the swath profiles method, showed a morphological difference between the eastern and western slopes of the axial chain, which develops along the Italian-French border line. The western slope (Italian part) is characterised by a greater relief energy, maximum elevation and depth of incision than the French slope. Moreover, a very marked orographic maximum was observed in the eastern part of the chain. The same analysis carried out with three parallel swath profiles in the area of the M. Matto-Argentera-Rocca dell'Abisso (MAA area) (south-east Italian part of the Massif) confirmed the presence of an orographic culmination with a direction parallel to that of the axial chain. This orographic culmination was also in agreement with a morphotectonic lineament, Colle del Sabbione-Colle del Chiapous Lineament (CSCC Lineament), which crosses the Massif for a distance of about 50 km. In the MAA area the normalisation of the topography showed the presence of an alignment of the main peak elevations, in agreement with the direction of the orographic culmination and the CSCC Lineament. The study of the drainage network of the Argentera shows that the hydrographic basin of the T. Gesso (MAA area), only in part that of the Vesubie (French slope), has a general drainage direction (trans-orogenic) considerably different from that of the other basins of the Massif (intra-orogenic). An examination of the relief data, geomorphologic-structural considerations and the known tectonic data, suggest that the orographic maximum within the axial chain corresponds to the morphological culmination of the hanging wall of a SW vergent thrust of the crystalline basement. The processes of exumation acting on the crystalline basement thus constituted generated in the Italian slope of the SE part of the Argentera a dishomogeneous relief, with steeper slopes, more incised network and a general phenomenon of retrogression of the watershed. The geomorphological evolution of this part of the Massif shows therefore that the process of tectonic uplift of the Argentera Massif occurred differentially.