Post collisional transpressive tectonics in northern Sardinia (Italy)

The aim of this work is to review and synthetize the geological and structural analysis performed in the Variscan Basement of Northern Sardinian during the last ten years and to add new preliminary data on the Anglona-SW Gallura area. A transpressive crustal-scale deformation (D2), is documented in the Variscan Basement of northern Sardinia. A shear deformation parallel to the belt, overprinting previous D1 structures related to a top-to-the S and SW nappe stacking, has been recognized. The L2 stretching lineation points to an orogen-parallel stretching and to a general change in the tectonic transport from D1 to D2 deformation phases. D1 phase developed during initial frontal collision whereas D2 deformation was characterized by dextral shearing. In this sector of the Variscan belt exhumation is due to continuing compression with an increasing component of horizontal displacement developed in a regime of decreasing pressure. The D2 transpressional deformation enhanced telescoping of the Barrovian isogrades and the exhumation of the low-to medium-grade metamorphic rocks. The overall change of the shortening direction in a large sector of an orogenic belt with the occurrence of increasing orogen-parallel displacement, may be regarded as a general mechanism affecting the exhumation of rocks and preventing the overthickened and thermally softened collisional crust from undergoing a diffused gravitational collapse. The rotation of nearly 90° of the tectonic transport in Sardinia during collisional and post-collisional stages could be related to paleoposition of the Corsica-Sardinia block, close to southeast France and northeast Spain, and to the development of the Ibero-Armorican arc.