Segmentation and mechanism for subsidence across the western Calabria continental margin, south-eastern Tyrrhenian Sea

The most relevant geologic features across the continental margin offshore western Calabria and its Neogene to Recent sedimentary and tectonic evolution are reconstructed using high-resolution coupled with high-penetration seismic lines. Data and interpretations we present offer an opportunity to investigate the influence of the roll-back and retreat of the NW-dipping subduction of the Ionian plate underneath Calabria on vertical movements in the overlying upper crust. Seismostratigraphic analysis was used to define seismic units. To assign ages to the sedimentary units, a key role was played by the Messinian horizon. Across the margin the major sedimentary units vary in thickness, number of seismic units and post late-Messinian tectonic deformation. On this basis, the margin has been divided into three distinct segments separated by narrow sub-vertical discontinuities. The NW- segment extends from the continental shelf of Calabria to the morphological high bordering to the west the Paola Basin, a NNW-SSE elongated basin filled by Plio-Pleistocene sediments more than 4.0 s thick. Here, we have distinguished four seismic units corresponding to sedimentary or crystalline rocks, pre late-Messinian in age, and three seismic units of Plio-Quaternary age. The central segment extends along the central sector of the margin. Here four seismic units have been identified. The lower one, tentatively attributed to the crystalline and metamorphic rocks and their Cenozoic terrigenous cover related to the Kabilian-Calabrian units, is unconformably overlain by the Messinian horizon. A number of closely spaced, mainly land- and sea-ward dipping listric faults with limited vertical slip, offset Plio-Pleistocene and older horizons. The SE-segment reaches to the west the oceanic sector of the Marsili Basin. Here, the Plio-Pleistocene seismic units appear to be strongly deformed by post - Late Messinian compressional or transpressional tectonic events. Geometries of reflectors in the continent-oceanic transition zone suggest that they represent the seismic expression of buried volcanic body. Data we presented suggests that: limited vertical slip occurs along normal and reverse faults detected at the border and inside the sedimentary infilling of the Paola Basin. Thus, mechanisms for subsidence affecting this area since the Late (?) Neogene significantly differ from extensional and/or compressional processes responsible for formation of basins along the Sardinia and in the north Sicily continental margins. Taking into account the pattern of the sedimentary infilling, the shape of the basin and its position in the regional context, we propose that the Paola Basin developed approximatively near the northern edge of the Ionian slab where tearing of the lithosphere is expected. Moving toward the continent-oceanic transition zone, the Calabrian margin may be partitioned into three segments characterised by different post Late-Messinian tectonic deformation and separated by localised strike-slip fault zone. It has been proven that strain across continental margin in oblique plate convergent setting is frequently partitioned in discrete strike-slip fault system and zone of diffuse deformations. Therefore, segmentation of the margin could be correlated with changes along strike in the dip and/or age of the Ionian oceanic lithosphere subducted underneath Calabria.