Conclusions
The Southern Apennines thrust belt developed during Neogene and Quaternary times along the eastward-retreating west-directed subduction of the Apulo-Adriatic lithosphere. The development of the Southern Apennines accretionary prism occurred through the off-scraping and incorporation at the subduction zone of the Meso-Cenozoic sedimentary covers (essentially pelagic units and shallow water carbonates) located along the Apulo-Adriatic passive margin, and associated active margin deposits. Since the Early Miocene, the accretionary prism migrated from west to east. Contractional deformations were followed by coeval extensional faulting which, progressively, cross-cut the thrust pile.
The main geological units incorporated in the Southern Apennines are from bottom to top in the thrust pile that corresponds to an east-to-west transect in the original paleogeography: i) the Apulian carbonate platform, ii) the Lagonegro-Molise basins, iii) the Apennine carbonate platform, and iv) the internal oceanic to transitional Liguride-Sicilide basinal domains (internal nappes).
The unquestionable evidence that about 190-210 km of crystalline basement (the former substratum of the allochthonous units) are missing, strongly supports the westward subduction of the Apulo-Adriatic continental lithosphere under the Southern Apennines. This geodynamic interpretation is also corroborated by several independent geophysical datasets.
Notwithstanding the wealth of subsurface data provided by the intense hydrocarbon exploration and the results of good quality structural and stratigraphic researches, the Southern Apennines structural setting could be effectively constrained only to a depth of about 10 km. The deeper setting is indeed still a matter of scientific debate. The two major unresolved issues regard: i) the shortening within the Apulian carbonate platform units, and ii) the degree of involvement of the Apulian crystalline basement. As a result both thin- and thick-skinned interpretation have been proposed.
However, if both thin- and thick-skinned are cross-checked against well documented tectonic, geophysical and geochemical features it emerges that the thin-skinned model is generally more consistent with the available data. Although it remains possible that the upper few kilometres of the Apulian basement could have been involved in thrusting, a thick-skinned interpretation (characterised by the development of basement slices tens of kilometres thick) is unable to coherently explain the overall geodynamic setting, the estimated “uplift of rock” rates, the observed maturity trends in the Apulian carbonates, and the Late Pliocene-Early Pleistocene front advance of the allochthonous nappes.
In the preferred thin-skinned model, about 90 km of shortening can be attributed to the Apulian thrust units. The total shortening of the allochthonous units (i.e., Apennine and Apulian Carbonate platforms and Lagonegro basin) is estimated to be greater than 280-300 km, a value relatively consistent with the length of the slab subducted beneath the Southern Apennines imaged by seismic tomography.