Applying thick-skinned tectonic models to the Apennine thrust belt of Italy: Limitations and implications

Fold-thrust belts are commonly interpreted as “thin-skinned” structures, developed above a detachment with the underlying basement remaining undeformed. However, in many areas, particularly where compressional tectonics was preceded by rifting, models of basement fault reactivation may be more appropriate. The contrasts between “thin-skinned” and deep-rooting, inversion-dominated deformation in building fold-thrust complexes are investigated using a case-history from the Italian Apennines. Three sectors were chosen to represent the marked lateral variations in structural style evident in the thrust belt. The outer portion of the Marche (in the north) is contrasted with a section through the Lucanian Apennines in the south and with the Molise district of the Central Apennines. The Marche structures are readily explained in terms of inversion, a model that is consistent with new deep seismic data onshore and conventional seismic from the nearby Adriatic sea. The displacements implicit for the inversion model are a factor of five less than for existing “thin-skinned” interpretations. However, these styles are not applicable throughout the Apennines. Well data in the Southern Apennines of Lucania demonstrate large-scale thin-skinned thrusting with 57 km of horizontal displacement since earliest Pliocene times. This includes 14 km of shortening that ramps up through the buried Apulian platform carbonates. These deeper structures may be restored using ramp-dominated thrust geometries. The Molise sector shows broadly the same structural style as for Lucania: Allochthonous shallow-water carbonates and pelagic basin units overly the carbonates of the Apulian platform, with the major difference being that here the pelagic basin units are detached at the level of the Oligocene-lower Miocene Argille varicolori. In this setting the Apulian carbonates may be restored using only 5 km of displacement. The overlying allochthon probably accommodated about 45 km displacement since the earliest Pliocene. Therefore the Apennines show differing structural styles with differing displacements along their length. Thick-skinned thrusting models may be applied to the Marche and to structures in the buried Apulian units