Conclusions
The approximately 200-million-year history of Adria depicts the evolution of a lithospheric slab that had a critical importance in the Europe-Africa relationship. Between the stable Europe, with a thicker continental lithosphere, bounded to the south by the Tornquist-Teyssere fault, and the northern margin of the stable Africa, bounded by the Atlas system of faults, lies a more mobile belt, affected by the Variscan and Alpine orogeneses. The time span considered in this paper covers the interval between these two major deformation events. Adria was basically connected with Africa. During the Permian, it was involved mostly with its northern part in the dextral megashear between Laurasia and Gondwana, which attenuated and eventually ceased during the Middle Permian. When this major transcurrent event was over, Adria remained an African Spur, even if affected by some rifting in Sicily and in the Ionian area. Evidence for a Permian oceanic way, early detaching Adria from Africa is considered not conclusive, and the presence of deep trenches along the rifting activated during the megashear activity are considered as sufficient to explain the deep-water faunal association described in the Permian of Sicily. From the Late Permian to the early Middle Triassic, the Adria margin evolved as a continental passive margin, especially toward the east, facing a branch of the Tethyan Ocean, probably the Palaeo-Tethys. While in the northern and central Apennines the crustal activity during the Middle Triassic to early Norian was attenuated, in the present Southern Alps it was registered as a more intense and complex geodynamic activity, with high subsidence, sedimentary productivity, and significant volcanic activity. Interpretations of these events are not unanimous and should be related to the western terminations of the Palaeo-Tethys Ocean. However, knowledge and interpretation of the belt between Turkey and the Balkan peninsula are far to be clearly understood and beyond the scope of this paper. With the end of the Carnian-early Norian, a new geodynamic event occurred, represented by the Central Atlantic rifting and its eastward propagation contouring the northern margin of Adria. It should be noted that the propagation was not connected to the trenches of Sicily and the Ionian Sea, which had already an attenuated continental crust, but was opened to the north of Adria. The new passive margin was, since the Norian, facing the area that in the Middle Jurassic gave way to the spreading of the Ligurian-Piedmont Ocean. In the Southern Alps and in the Northern and Central Apennines, the passive margin evolution is preserved. In the present paper, this was described mostly for the Southern Alps, where alpine tectonics disrupted the original relationships less. The passive margin evolution registered all of the phases from rifting to spreading until toward the end of the Early Cretaceous, when the opening of the Southern Atlantic Ocean pushed Africa to rotate anticlockwise and approach Europe. The Adria margins first involved in the convergence emerged, and its terrigenous products were deposed in basins, mostly in Lombardy, on the rear of the deformated ridges. Far from the margin under deformation, as in the eastern Southern Alps and central Apennines, carbonate production and deposition continued.