P-T evolution vs numerical modelling : a key to unravel the Paleozoic to early-Mesozoic tectonic evolution of the Alpine area

The pre-Alpine continental crust of the Alps preserves Permian-Triassic magmatic and high-temperature (HT) metamorphic evolutions, which overprinted records of Variscan subduction and collision-related metamorphism. The occurrence of numerous Variscan eclogites in the pre-Alpine continental crust, presently belonging to different structural domains, indicates that part of the Variscan suture zone occurs in the Alpine belt. The late Variscan evolution took place from 340 to 300 Ma, and therefore the igneous and metamorphic signatures up to Upper Carboniferous may represent the record of the late orogenic evolution. On the contrary, different authors interpreted the HT metamorphism associated with gabbro to granite intrusions younger than 290 Ma as the effect of Permian-Triassic late-orogenic collapse or continental rifting. The goal of this study is to reduce the ambiguity about the geodynamic significance of the Permian-Triassic HT metamorphism and igneous activity in the Alpine continental crust, with the support of numerical modelling of: ocean subduction, continental collision, lithospheric detachment and subsequent gravitational thermal relaxation. Comparison of the model predictions with structural and petrologic data has driven the successive model refinements to improve the fit. The best fit model predictions show a rather good agreement with natural data (coincidence of age, P-T values and rock compositional affinity) up to late-Variscan times. The poor agreement during the Permian-Triassic evolution suggests that, with respect to the thermal state established during the post-collisional gravitational evolution, an additional positive heat anomaly is necessary to induce the thermal state indicated by natural P-T estimates.