Tectonics, magmatism and geodynamics of Italy: What we know and what we imagine

Eugenio Carminati , Michele Lustrino, Marco Cuffaro, and Carlo Doglioni

The Cenozoic geological evolution of the Italian area is characterized by the formation of two major mountain chains - the Alps to the north and the Apennines throughout the peninsula – plus the opening of two oceanic basins (the Ligurian-Provençal and the Tyrrhenian Sea). Associated with the formation of these two belts, a volumetrically important and chemically complex magmatic activity developed. The Alps and the Apennines show very different styles of evolution: the Alps display double-verging growth, with the involvement of large volumes of basement and the exhumation of metamorphic rocks (thick-skinned tectonics). On the other hand, the Apennines are a single-verging belt, mostly characterized by thin-skinned tectonics and associated to a radial "eastward" translation (coupled to extensional tectonics in the Ligurian-Provençal, Tyrrhenian, and western Apennines areas). The Apennines generated an arc from the northern Apennines down to Sicily, possibly merging with the Maghrebides along the northern Africa coast. The different evolution of the Alpine and Apenninic belts is mirrored by the different geometry of the respective foredeep or foreland basins (shallow in the Alps and deep in the Apennines), as recorded also by the dip of the foreland monocline (shallow in the Alps, 2-4°, and steeper in the Apennines, 6-15°).

The paradox is evident: the higher the belt, the thinner the foreland basin. The Alps consist of rocks belonging to the continental margings of the European and Adriatic-African plates, as well as remnants of Mesozoic intervening ocean(s). On the other hand, the Apennines, with the exception of the Calabro-Peloritani arc and other scattered basement outcrops, are mainly made up of rocks of Adriatic origin (Mesozoic Laziale-Abruzzese and Apulian carbonate platforms plus basinal successions), with subordinate ophiolites. From a magmatological point of view, the Alpine magmatism is essentially concentrated in a relatively narrow area, the so-called Insubric Lineament and in a relatively short time (mostly ~32-24 Ma). On the other hand, the Apennines-related igneous activity spans a larger time range (essentially from 22 Ma to Present), with several peaks in magma production. This magmatism took place over a much wider area, characterized by variable lithospheric thickness, Moho age and depth.

On the basis of thermo-tectonic, magmatological, and plate-kinematics constraints, a geodynamic evolutionary model of the Italian area is proposed. We suggest that three subduction zones have been active and have consumed oceanic and, partially, continental lithosphere: the Alpine subduction zone, with the European plate under-thrusting the Adriatic microplate; the Apenninic subduction zone, with the ancient (Mesozoic?) Ionian/Mesogean oceanic lithosphere and the Adriatic micro-plate under-thrusting westward the European plate; and the Dinaric subduction zone, with the Adriatic micropate under-thrusting northeastward the European plate. Such a geodynamic scenario is summarised in a movie, spanning the last 50 Ma.