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

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 metamorphism at 315 ± 1.3 Ma (U–Pb, monazite) in mylonitic Silurian orthogneisses. The NW–SE dextral 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

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

The exhumation of the Variscan High Grade Metamorphic Complex of Sardinia has been driven by a wide dextral shearing which reached middle crustal levels at 325 \ub11.3 Ma and caused partial melting. The migmatization process has been followed by the emplacement of syn-tectonic granites dated at 316 \ub12 Ma, 318 \ub13 Ma and 317 \ub12 Ma which produced contact metamorphism at 315 \ub11.3 Ma in mylonitic Silurian orthogneiss. The NW-SE dextral shear zone of the Capo Ferro area (NE Sardinia) shows remarkable petro-tectonic analogies 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 is 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 between Gondwana and Laurussia plates during the Middle-Upper Carboniferous

Contact metamorphism in Middle Ordovician arc rocks (SW Sardinia, Italy): new paleogeographic contraints

In the early Cambrian Bithia Formation in the Variscan foreland of Sardinia, a Middle Ordovician granitic intrusion (478\u2013457 Ma) is hosted by marly metasedimentary rocks that were affected by high-temperature (HT) metamorphism. A detailed structural\u2013petrographical transect was conducted through the granitic intrusion and its host rocks. Field data and relationships between HT/low-pressure (LP) mineral assemblages in the metasedimentary rocks (Grt + Wo + Ves in carbonate lenses and And in pelite) demonstrate that the study area was affected by a polyphase HT overprint (I: T = 520\u2013620\ub0C at XCO2 = 0.1, P: 0.2\u20130.4 GPa; and II: T = 600\u2013670\ub0C at XCO2 = 0.1, P = 0.2\u20130.4 GPa) that pre-dates the Variscan tectonic, metamorphic, and igneous phases. In the Canig\uf2 or Canigou Massif (Eastern Pyrenees), the Somail Massif (Montagne Noire), and the Ruitor Massif (Internal Massifs, NW Alps), Middle Ordovician orthogneiss with relict igneous textures are deciphered despite being overprinted by Variscan amphibolite-to-granulite-facies metamorphism and subsequent Alpine low-grade metamorphism. Comparisons of associated igneous and metasedimentary rocks in the Sardinia foreland with the High-Grade Metamorphic Complex in the Variscan Axial Zone and the Canigou Massif indicate a convergent Middle Ordovician evolution that was overprinted by HT Variscan metamorphism

Contact metamorphism in Middle Ordovician arc rocks (SW Sardinia, Italy): New paleogeographic constraints

In the early Cambrian Bithia Formation in the Variscan foreland of Sardinia, a Middle Ordovician granitic intrusion (478–457 Ma) is hosted by marly metasedimentary rocks that were affected by high-temperature (HT) metamorphism. A detailed structural–petrographical transect was conducted through the granitic intrusion and its host rocks. Field data and relationships between HT/low-pressure (LP) mineral assemblages in the metasedimentary rocks (Grt + Wo + Ves in carbonate lenses and And in pelite) demonstrate that the study area was affected by a polyphase HT overprint (I: T = 520–620 °C at XCO2 = 0.1, P: 0.2–0.4 GPa; and II: T = 600–670 °C at XCO2 = 0.1, P = 0.2–0.4 GPa) that pre-dates the Variscan tectonic, metamorphic, and igneous phases. In the Canigò or Canigou Massif (Eastern Pyrenees), the Somail Massif (Montagne Noire), and the Ruitor Massif (Internal Massifs, NW Alps), Middle Ordovician orthogneiss with relict igneous textures are deciphered despite being overprinted by Variscan amphibolite-to-granulite-facies metamorphism and subsequent Alpine low-grade metamorphism. Comparisons of associated igneous and metasedimentary rocks in the Sardinia foreland with the High-Grade Metamorphic Complex in the Variscan Axial Zone and the Canigou Massif indicate a convergent Middle Ordovician evolution that was overprinted by HT Variscan metamorphism