The East Variscan Shear Zone: Geochronological constraints from the Capo Ferro area (NE Sardinia, Italy)

摘要

The exhumation of the Variscan High Grade Metamorphic Complex of Sardinia was driven by large-scale asymmetric shear zones which reached middle crustal levels at 325 ±1.3 (U-Pb, monazite) Ma. Exhumation was accompanied by heating and partial melting. The migmatization process was followed by the emplacement of syntectonic granites dated with U-Pb on zircon at 318 ± 3 Ma and 317 ± 2 Ma, which produced contact meta-morphismat315 ± 13 Ma (U-Pb, monazite) in mylonitic Silurian orthogneisses. The NW-SEdextral shear zone of the Capo Ferro area (NE Sardinia) is affected by partial melting, by granite emplacement and shows remarkable petrotectonic analogies to, and can thus be related to the East Variscan Shear Zone, a major intra-continental shear zone which was active in the southern European Variscides from 325 Ma to 315 Ma and that has been precisely dated with the U-Pb monazite system. The emplacement of migmatitic gneisses along large shear zones within this time interval is not restricted to Sardinia, but has also been observed in southern Corsica, in the French Massif Central, in the Western Alps and in central Spain. This pattern of shear zones is related to a complex geodynamic scenario, linked to the oblique convergence of the Gondwana and Laurussia plates during the Middle-Upper Carboniferous.