Growth processes and melange formation in the southern Apennines accretionary wedge

Abstract

The Southern Apennines owe their present geometry to the subduction of an Apulian continental lithospheric slab and are thus best interpreted as an accretionary wedge. Southward, the Apenninic thrust front branches on to the still active Ionian wedge, which is related to the present Calabro-Sicilian subduction. The interpretation of conventional seismic reflection profiles and exploration wells, combined with geologic field studies (biostratigraphy and structural geology), provide constraints for a geodynamic model for the post-Messinian growth of the Apenninic prism. Our model for the Apennines is a good analogy for submerged oceanic accretionary prisms; in both instances features such as out-of-sequence thrusts, underplating and duplexes are viewed as processes to explain the thickening of accretionary wedges. Syntectonic terrigenous deposits have accumulated in the synclines developed above the flats of Pliocene thrust faults. These depocenters represent piggy-back basins. Younger accretion at the eastern border of the accretionary wedge has led to a progressive uplifting and tilting of the already-emplaced thrust sheets, including a continous westward migration of the depocenters in the piggy-back basins during Pliocene and early Quaternary times. A contrary west-to-east migration of the depocenters locally occurred where preexisting flats of Pliocene thrust faults have been refolded rather than only being rotated. Dewatering processes and effects of overpressures on undercompacted sediment deformations can also be studied in the southern Apennines. Melanges and broken formations form an important component of the trench, apparently restricted to the base of tectonic nappes. Listric normal faults are a major structural element which preserves, in combination with the erosion of topographic highs and resedimentation in the piggy-back basins, a uniform geometric shape (critical taper) for the prism. The age and location of these distensive or gravitational effects are also discussed.