Crustal tectonostratigraphy and geodynamics of the southern Apennines from CROP and other integrating geophysical-geological data

Using CROP geophysical data integrated with other information, a new lithospheric seismogeological section across the Southern Apennines, from the Marsili Basin in the Tyrrhenian sea to the Adriatic coast of Apulia, has been reconstructed. This section provides a clear regional deep subsurface imaging of the tectono-stratigraphy, and interpretation of the CROP network allows us to propose a new, much more constrained, geodynamic model. Across the Southern Apennines thrust belt, from the young (Quaternary) back-arc basin of Marsili to the Apulian Permo-Mesozoic foreland, various tectono-stratigraphic units with different histories are imaged and described. The first part of the paper comments on the geological data obtained by geological fieldwork carried out mainly in the Lucania sector, integrated with available subsurface data(seismic, borehole); the second presents the new interpreted crustal-lithospheric seismogeological section. From the Tyrrhenian ocean basin to the outerward undeformed Apulian foreland, the Southern Apennine thrust belt is formed by: (a) a deformed European crustal fragment, detached from the Corso-Sardinian block in the Tyrrhenian stage; (b) a deformed crustal block of the Etrurian Promontory (NW Adria corner), which collided with the Apulian slope, whose Mesozoic cover gave rise to the Apennine platform thrust-sheets. Between(a) and (b), Alpine Tethydes Units(Ligurides), detached from subducted Alpine Tethys slab, were closed in the Balearic stage; (c) A wedge of Ionian Tethydes or Ionides (Lagonegrese) stripped off the subducted Ionian slab and thrust obliquely onto Apulia (over Lower Pliocene cover) in the Tyrrhenian stage; (d) two main families of flysch: the Albidona group and the Gorgoglione more external flysch group, plus the Numidian flysch derived from displaced Paleozoic basal quartzites of denuded Adria–Africa zones (Etrurian and Panormid promontories); and e) rooted or severely displaced buried thrust structures of the Apulian platform. A well-constrained description of the tectono-stratigraphy of the units which compose the allochthonous nappe is given, and some geological sections are illustrated. The field geology with careful biostratigraphic control shows that the units of the Southern Alpine chain (SAC), deriving from sedimentary sequences originating in the Alpine Tethys realm, started to deform in the Late Oligocene and continued later on involving the external domains. The reconstructed lithospheric seismogeological section exhibits clearly that two main tectonostratigraphically distinct complexes are present on the onshore Southern Apennines thrust belt: (1) a buried Apulian platform, deformed by Pliocene compressive tectonics, which produced folds and reverse faults, mostly of relatively moderate horizontal displacements, where a major part of the thrust features remain substantially rooted; (2) a strongly tectonized composite nappe over Apulia, made up of allochthonous units and internalexternal- reworked flysch. A stack of allochthonous crustal blocks colliding with the Apulian slope on the Tyrrhenian side characterizes the Tyrrhenian margin.Careful interpretive seismic reprocessing allowed us to obtain for the first time a clear seismic imaging of the subducted Ionian slab, the buried slope of Apulia on the Tyrrhenian side, and the stacked allochthonous crustal blocks. From the Marsili basin to the Apulian foreland, the major crustal features have been identified and their tectono-stratigraphy outlined. On the Apulian slope, a previously formed tectonic stack of two crustal fragments, which took part in the closure of the interposed Alpine and Ionian Neotethyan oceans, collided. The Corso-Sardinian block in the Balearic stage (Late Oligocene–Early Miocene) collided with the northwestern Adria margin with thrusting of the Alpine Tethydes over Adria (Etrurian Promontory). In the Tyrrhenian stage (Middle Miocene to Present) the stacked Corso-Sardinian and Etrurian fragments followed the Ionian slab retreat, closing the interposed basin with tectonic transport of the Ionian ocean cover (“Ionides”, “Lagonegrese” in the literature) over the Apulian platform. The Bradanic foredeep and the Mt. Alpi Unit are connected to the two major transcrustal thrust faults in the examined area. The total crustal shortening of the Apulian platform during the Southern Apennines tectonics amounts to about 30 km, very much less than the observed shortening of the Adria plate during the Northern Apennines tectonics (about 150 km).