Slab retreat and active shortening along the central-northern Apennines

The Quaternary geodynamic evolution and the tectonic processes active along the Central and Northern Apennines thrust fronts and in the adjacent Paclane-Adriatic foredeep domains are analysed and discussed. A reinterpretation of the available geophysical and geological data reveals that the south-eastward prolongation of the Apennines thrustfiront in the Adriatic Sea is most likely located along the north-eastern side of the Adriatic ridge, i.e., in a more external position with respect to traditional interpretations. Further south, the Apennine thrust front is segmented in correspondence with the Tremiti lithospheric right-lateral transfer zone. This new interpretation of the Apennine thrust front bears some relevant implications since it rejuvenates to Late Quaternary the most recent contractional deformations in its Adriatic portion. This is consistent with the Late Quaternary activity of the buried thrust-related folds associated with the Apennine front along the Marche coastal belt and in the Po Plain documented by geornorphological analysis and by seismic reflection profiles. Moreover, active shortening associated with the Apennines accretionary prism in the Po Plain and in the central and northern Adriatic Sea is documented by GPS data and by historical and instrumental seismicity. The Quaternary evolution of one of the active thrust-related folds recognised in the Po Plain subsurface (the Mirandola anticline) has been investigated in detail by backstripping high-resolution stratigraphic data. Our results show decreasing relative uplift rates during the Quaternary. However, tectonic relative uplift rate of about 0.16 mm/a can still be recognised during the last 125 ka. Horizontal shortening fasterthan 1 mm/a should be expected in agreement with available GPS data. Furthermore, the SW-ward (or W-ward) increasing dip of the foreland monocline in the Po Plain and in the central-northern Adriatic and the asymmetric distribution of the Quaternary to Recent subsidence indicate a still active flexural retreat of the subducting lithosphere in these domains. The Quaternary to Recent flexural retreat of the subducting Adriatic lithosphere and the related frontal accretion of the Apennines prism are framed in a coherent geodynamic scenario characterized by a retreating west-directed subduction zone, which is the natural evolution of the Neogene geodynamic history.