The Ottone-Levanto Line of Eastern Liguria (Italy) uncovered: a Late Eocene-Early Oligocene snapshot of Northern Apennine geodynamics at the Alps/Apennines Junction

The Northern Apennine orogenic belt developed during subduction and collision between the Europe and Adria plates. The northernnmost sector of the nappe pile is dissected by several tectonic lines, whose kinematics and age are crucial for the understanding of the Northern Apennine evolution, and its mutual relationships with the neighbouring Alps. Between these, the Ottone-Levanto line still lacks an unambiguous geodynamic interpretation, because of lacking of well-exposed outcrops. We describe unique fault rocks exposures representative of the Ottone-Levanto line whose structural features indicate deformation with components of contraction through top-to-the-NE thrusting and contemporaneous top-to the-SW sinistral/dip-slip shearing. The collected data coupled with regional and map-scale evidences indicate that the Ottone-Levanto line acted as a sinistral transpressional shear zone during the Late Eocene-Early Oligocene. Placing our data in the regional context allows correlating the Ottone-Levanto line with surrounding lines dissecting the Alpine-Apennine junction. We propose that the Ottone-Levanto developed in a conjugate system during collision and northward displacement of the Adria plate, resulting in east- and westward thrusting of the Alpine Apennines orogenic core.