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, th e collisional phase of the Variscan orogeny during Late Carboniferous and P ermian times was followed by magmatic intrusive and effusive activity and s edimentation into intracontinental, alluvial to lacustrine basins originate d by wrench- to normal-fault systems. The first volcanic cycle (generally L ate Carboniferous-Early Permian in age) is represented by early calc-all;al ine andesites and rhyolites, in variable amounts, and by following large vo lume of rhyolites, and by dacites. Both andesites and rhyolites show K-norm al and high-K calc-alkaline character. The origin of the liquids of the fir st cycle is ascribed to partial melting processes at the mantle-crust inter face 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 occ urred in a (trans-)tensional regime. The second magmatic cycle is represent ed by alkaline magmatism, and exhibits typical anorogenic features consiste nt 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-organizatio n of plates that evolved during Late Triassic times to the neo-Tethyan rift ing. In both cycles, important differences in timing, areal distribution an d outpoured volumes arise. (C) 1998 Elsevier Science B.V. All lights reserv ed.