Structural and palaeogeographic lineaments of the Variscan cycle in Sardinia

Abstract

In the Variscan orogen of Sardinia it is possible to distinguish: (1) A Southwestern zone (foreland), restricted to the SW of the Cenozoic graben of Campidano, with slight metamorphism and minor folding without important overthrusts. (2) A central zone that runs across the entire island from Nurra to Sarrabus, characterized by important overthrusts and a rather uniform metamorphism never exceeding the greenschist facies. The metamorphism grades towards the NE into the higher-metamorphic area. (3) The Northeastern zone (granitized root zone) that includes the northern tip of the island and is characterized by the superimposition of several metamorphic episodes and by tectonic events that have intensively remobilized the pre-Variscan basement. A conventional boundary between the two last belts may be drawn along the NW-SE line joining Stintino and Dorgali. Furthermore, there seems to be a parallellism between post-Cambrian palaeogeographic domains and Variscan tectono-metamorphic zones. The absence of ophiolite associations, the Ordovician magmatism, the Silurian one with continental alkaline affinity and the Variscan metamorphism of low or intermediate pressure suggest that the Variscan orogenic cycle in Sardinia had an ensialic evolution. The structural style of the different zones, the asymmetry of the belt, the division into metamorphic zones and the relationship between crystallization and deformation suggest also that the northeastern Sardinian Variscan belt represents the portion of the crust deeply subducted along intracontinental shear zones dipping towards the NE.