The rotation of the direction of tectonic transport by nearly 90° from D1 to D2 has been observed by Carosi & Palmeri, (2002), in northeastern Sardinia. A similar tectonic behaviour has been described both in the northwest (Carosi & Oggiano, 2002) and in the south of Sardinia (Lünuburg & Lebit, 1998; Conti et al., 2001), suggesting that such kinematic events are clearly a common feature in the whole island.
The regional scale change in the direction of the tectonic transport in Sardinia can be interpreted as the expression of a change from frontal to oblique collision from D1 to D2. However, tectonic constraints for plate tectonic reconstruction at the end of the Paleozoic are too limited for the Corsica-Sardinia block and surrounding terrains and the tectonic scenario is still debated and poorly constrained (presence of a suture, numbers of oceans, plate involved) to test this hypothesis.
An alternative explanation, with the limitation for the lacking of detailed correlations between Sardinia and the other portions of the southern Variscan belt, has been proposed by Carosi & Palmeri, (2002), considering the position of the Corsica-Sardinia block before the Miocene counterclockwise rotation (Barnolas & Chiron, 1996 with references therein). According to Arthaud & Matte, (1977), Ricci & Sabatini, (1978), Matte, (1986) and Barnolas and Chiron, (1996), the northernmost part of Sardinia was connected to southeastern France during the upper Paleozoic. In this paleo-position, the activity of a transpressional shear zone in northern Sardinia could fit with the indentation between Armorica and Gondwana as proposed by Matte & Ribeiro, (1975), Brun & Burg, (1982), Ribeiro et al. (1995) and Dias & Ribeiro (1995). During the Carboniferous, a dextral transpression began to predominate in the Armorican branch of the arc, while in the southern branch southward thrusting predominated. Moreover, the indentation of the Cantabrian block (Dias & Ribeiro, 1995), during and after the thickening stage of the belt, caused tightening of the arc inducing an increasing strike-slip component of deformation in the limbs. This could have led to the generation of ductile transpressional shear zones while the crust was thermally weakened, because of the high temperatures after the D1 thickening stage. In some sectors of the Variscan belt, such as northern Sardinia, transpressional deformation affected medium pressure rocks and their exhumation history.
The change in tectonic transport by nearly 90°, from perpendicular to parallel to the belt, deeply influenced the fate of large portions of the thickened crust before its gravitational collapse.
The change from frontal collision to orogen-parallel displacement may be a common feature in the orogenic belts, in which indentation tectonics occurs or there is a change of relative kinematic of the plates. This change may play an important role in the equilibration, exhumation and the tectonic history of metamorphic rocks in orogenic belts.
Ricci et al., (2004), emphasized the higher exhumation rate of migmatites with respect to lower-grade rocks during the first stages of exhumation that can be attributed both to a decreasing strength of the lower crust and to the prevalent pure shear component in the developing transpressive regime.
The proposed tectonic evolution is able to explain an initial high rate of exhumation with dip-slip movement for the deepest rocks followed by slow exhumation rate up to higher structural levels with a major component of horizontal movement compatible with Barrovian metamorphism during decreasing pressure.