Crustal evolution and basement elements in the Italian area: palaeogeography and characterization

Identification of different basement components within the Mediterranean region (including Italy) is usually based on palaeotectonic restorations starting from the Triassic continental plate assembly called Pangaea. In this way, older crustal evolution during both Paleozoic and Precambrian times is simply neglected. Here, an attempt is made to start restoration from the late Precambrian Pangaea so as lo consider the roles played by Panafrican, Hercynian, Cameroon and Alpine crustal consolidation cycles. Following the Panafrican consolidation, there is a substantial southward time migration of the tectogenesis in the Mediterranean area (Fig. 2A). However, the major control of the crustal evolution in the area is related to recurrent inversion (dextral to sinistral and viceversa) in the transform rifts cyclically affecting the area (Figs. 1 and 2B). Of primary importance in this scenario is a careful evaluation of the Permian (and Triassic) dextral rifts as opposed to the Jurassic sinistral] one. A set of new palaeogeographic palaeodynamic maps (Figs. 4-7) of the late Carboniferous to middle Permain time interval are presented ai both the regional and hemi-global levels. The maps suggest 1) a persistent late Devonian to early Permian dextral strike-slip kinematics of the Hercynian orogen; 2) a relative independence of the widespread small scale late Carboniferous transtensional regime from the large-scale Permian (and later Triassic) rift; 3) a major dextral strike-slip rift belt, striking from the Persian Gulf to Sicily, Tunisia. Texas and Bolivia, dividing Laurasia from Gondwana for some tens of Ma, and resulting in the formation of a narrow seaway floored with oceanic crust in the present Ionian and eastern Mediterranean seas. Increasing stratigraphic and facies evidence of early to mid Permian pelagic deposits support the reconstruction above, which is also consistent with mid to late Triassic marine facies distributions. A short characterization of the main basement and Paleozoic elements of the Italian area in terms of overall geological evolution is given. Three elements are distinguished in the Southern Alps (Carnic Alps, Venetian and central-western areas), four in the Northern Apennines (Elba-P. Bianca-Massa, Alpi Apuane-M. Pisano, southern Tuscany and Cerreto areas), two in Sardinia (Iglesiente-Sulcis and remaining areas) and two in Calabria (part of Sila and the remaining composite areas). Finally, on the basis of these various types of data, the following crustal zonation of the Italian and central Mediterranean area is suggested: I ) Baikalian-Panafrican, 2) European Hercynian, 3) thinned Herecynian, 4) Ionian Permo-Triassic fossil oceanic, and 5) Balearic Miocene and Tyrrhenian Plio-Pleistocene new oceanic zones.