The Variscan post-collisional volcanism in Late Carboniferous–Permian sequences of Ligurian Alps, Southern Alps and Sardinia (Italy): a synthesis

In the considered wide sector of the West-Mediterranean southern Europe, the collisional phase of the Variscan orogeny during Late Carboniferous and Permian times was followed by magmatic intrusive and effusive activity and sedimentation into intracontinental, alluvial to lacustrine basins originated by wrench- to normal-fault systems. The first volcanic cycle (generally Late Carboniferous-Early Permian in age) is represented by early calc-alkaline andesites and rhyolites, in variable amounts, and by following large volume of rhyolites, and by dacites. Both andesites and rhyolites show K-normal and high-K calc-alkaline character. The origin of the liquids of the first cycle is ascribed to partial melting processes at the mantle–crust interface telescoped within a thickened crust. The melting is considered as the consequence of thermal re-equilibration following isostatic disequilibrium and the subsequent collapse of the orogenic belt; the ascent of liquids occurred in a (trans-)tensional regime. The second magmatic cycle is represented by alkaline magmatism, and exhibits typical anorogenic features consistent with a rifting regime. This event was no more related with the collapse of the Variscan belt, but rather to the post-Variscan global re-organization of plates that evolved during Late Triassic times to the neo-Tethyan rifting. In both cycles, important differences in timing, areal distribution and outpoured volumes arise.