Estensione alla sommità del cuneo orogenico appenninico: contatti tettonici elisionali nella Successione epiligure di M Barigazzo (Appennino settentrionale, prov. di Parma)

The work was planned to carry out a research program directed to define the collapsing conditions of the post-collisional orogenic wedge of the North-Western Apennines. The Mt. Barigazzo Epi-Ligurian succession unconformably overlies the Ligurids and consists of Monte Piano Marls (Lutetian-Priabonian) and Ranzano Formation (Priabonian-Rupelian) about 500 m thick. The field survey carried out in the Taro Valley area testified that Epi-Ligurian succession tectonically overlies the Ligurids. A gently NE-dipping tectonic boundary, between the uppermost portion of the Ranzano Formation and the Ligurids, displays an extensional deformation occurred when the Ranzano Formation was still unlithified. This low-angle deformation suggests a NE-gliding of the Mt. Barigazzo succession, probably during Neogene. This result may be applied to the tectonic framework of the Ligurids outcropping SW of Mt. Barigazzo area, where low angle detachment faults can be envisaged too. Then, similar Messinian extensional collapses are reported in more external area of North-Western Apennines orogenic wedge. Thus, the role of extensional processes in shaping the uppermost portions of the apenninic orogenic wedge should be reconsidered. This implies a precise dating of the extensional events and the understanding of their relationships with crustal scale accretionary orogenic processes.