Deep structure of the southern apennines as imaged by active and passive seismic data along the crop-04 (Crustal) reflection seismic profile

We combine active and passive seismic data to reconstruct a coherent picture of the deep crust beneath the Southern Apennines orogen. The Southern Apennines collisional setting is characterized by deep structural complexities, which have been here investigated through different seismic data from both active and passive surveys. Several geological reconstructions have been carried out in the last two decades to interpret the detected substructures, but failed to provide a univocal interpretation of the Apennine roots. At present, strong disagreements exist among geologists about the tectonic style of the chain in that portion of the Italian peninsula. In this study, we first combine five passive seismic datasets from the overall available literature and we then project them at relative depths on a co-located active seismic profile (CROP-04). The general aim of the study is to shed light on the Southern Apennines structure at depths greater than 25 km, where, through the adopted approach, an approximate shape of the lower crust and upper mantle structure can be delineated. Our results indicate the following: (1) during the Adriatic slab retreat, the crust along the Tyrrhenian margin was only marginally thinned (Moho depth about 28–30 km), much less than along the Tyrrhenian coast of the Northern Apennines and Calabria (where Moho depth has been found at 20–25 km); (2) the subduction process has locally been stationary for a long time, leading to the complete eclogitization of the subducted crust and total regeneration of the Tyrrhenian Moho; (3) subduction fluids underwent a complete migration out of the mantle wedge, as testified by the high velocities found in the upper mantle below the Moho in the Tyrrhenian region (observed nowhere else in the Apennine subduction setting).