HIDDEN TERRANES IN THE NORTHERN APENNINES, ITALY - A RECORD OF LATE CRETACEOUS OLIGOCENE TRANSPRESSIONAL TECTONICS

We propose that a very oblique or transpressional tectonic regime was dominant during the early (pre-collisional) orogenic evolution of the Northern Apennines (Late Cretaceous to Early Oligocene). This hypothes is resolves many inconsistencies in the previous reconstructions of th is orogenic belt, which were based on a classic model of orthogonal co nvergence between the European and Adriatic plates. The crucial lines of evidence that point to a major role of oblique tectonics in the str ucturing of the Northern Apennines are: (1) the plate tectonics framew ork, that indicates left-lateral oblique convergence along the Europe/ Adria plate margin; (2) the lack of a magmatic are during the entire p re-collisional convergent history of the chain (a time span >45 m.y., from Late Cretaceous to Early Oligocene); (3) the long (20 m.y.) resid ence time of turbidite sequences in the trench (the ''dormant'' trench ); (4) the multiple source areas of turbidites from both sides of the basin, and the associated coarse gravity deposits; (5) the opposite ve rgence of deformations in some oceanic units; (6) the unmatching strat igraphic features, distinct deformation and metamorphic histories betw een adjacent overthrust oceanic units (Ligurids), here interpreted as tectonostratigraphic terranes. Specific aspects of Apennine stratigrap hy and tectonics and the geometry and structure of the contacts betwee n the Ligurid Units suggest the existence of a number of terranes juxt aposed by transpression during the early (Late Cretaceous to Early Oli gocene) orogenic evolution of the chain.