Tectonics of the Dolomites (southern alps, northern Italy)

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In post-Variscan times the Dolomites underwent a number of tectonic events, which may be summarized as follows: Permian and Triassic rifting phases broke the area into NS trending basins with different degrees of subsidence. A Middle Triassic transpressive event then deformed the region along a N70°E axis, generating flower structures within the basement. Volcano-tectonic domal uplift and subsequent caldera formation occurred at the same time as the Late Ladinian magmatism. Early Jurassic rifting also controlled the subsidence which increased eastward. This long period of deformation was followed by a pre-Neogene (Late Cretaceous-Palaeogene ?) EW (ENE-WSW) compression which generated a W-vergent belt, possibly equivalent to the folded foreland of the Dinaric chain. A 70 km EW section of the Dolomites indicates shortening of at least 10 km. During the Neogene the Dolomites, as far north as the Insubric Lineament, were the innermost part of a S-vergent thrust belt: the basement of the Dolomites was thrust southwards along the Valsugana Line onto the sedimentary cover of the Venetian Prealps for at least 10 km. This caused a regional uplift of 3–5 km. The Valsugana Line and its backthrusts on the northern side of the central Dolomites generated a 60 km wide pop-up in the form of a synclinorium within which the sedimentary cover adapted itself mainly by flexural-slip often forming triangle zones. The shortening linked to this folding is about 5 km with Neogene thrusts faulting and folding pre-existing thrust-planes. On the north-eastern side of the Dolomites, Neogene deformation is apparently more strictly controlled by the transpressive effects of the Insubric Lineament and shortening of the sedimentary cover may be greater than in the central Dolomites. Minor deformation linked to the Giudicarie belt is present in the western Dolomites. The present structure of the Dolomites is thus the result of a number of tectonic events of different significance and different strike. Only a 3-dimensional restoration can unravel the true structure of the Dolomites.