The post-collisional tectonics in the inner zone of the Variscan belt of Corsica-Sardinia recorded a dextral transpression developed with an orogen-parallel tectonic transport. Recent works documented the presence of nearly parallel dextral and sinistral crustal-scale shear zones responsible for the exhumation of the metamorphic complexes. To constrain, for the first time, the timing of both shear zones and the timing of the transpressional shearing, zircons and monazites were collected for U-Th-Pb ages. Results indicate that the shear zones have been active at c. 320Ma in a transpressional setting, widespread in the Southern European Variscan belt

No abstract

In Corsica, continental units (the Lower Units) affected by high-pressure metamorphism represent the remains of the European margin deformed during the Alpine orogeny. In order to document how Alpine deformation and metamorphism changed along the European margin involved in the Alpine subduction, we selected three key areas: the Corte, Cima Pedani, and Ghisoni transects. The three transects show a broadly similar lithostratigraphy. They are characterized by a Variscan basement intruded by Permo-Carboniferous metagranitoids, and by a sedimentary cover including Mesozoic carbonates and middle to late Eocene breccias and sandstones. The three transects recorded a similar deformation history with three deformation phases. Thermo-baric estimations, instead, reveal that each unit was exhumed along an independent retrograde path within the orogenic Alpine wedge. In particular, the lowest units of the Lower Units stack were exhumed along an isothermal path, whereas those located at upper structural levels experienced progressive heating.

The Anglona and SW Gallura regions represent key places to investigate the tectonic evolution of medium- and high-grade metamorphic rocks cropping out in northern Sardinia (Italy). From south to north we distinguish two different metamorphic complexes recording similar deformation histories but different metamorphic evolution: the Medium Grade Metamorphic Complex (MGMC) and the High Grade Metamorphic Complex (HGMC). After the initial collisional stage (D1 deformation phase), both complexes were affected by three contractional deformational phases (D2, D3 and D4) followed by later extensional tectonics. The D2 deformation phase was the most significant event producing an important deformation partitioning that produced localized shearing and folding domains at the boundary between the two metamorphic complexes. We highlight the presence of two previously undocumented systems of shear belts with different kinematics but analogous orientation in the axial zone of Sardinia. They became active at the boundary between the MGMC and HGMC from the beginning of D2. They formed a transpressive regime responsible for the exhumation of the medium- and high-grade metamorphic rocks, and overall represent a change from orthogonal to orogen-parallel tectonic transport

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 crustalscale 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 topto-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.