TERTIARY STRUCTURAL RELATIONSHIPS BETWEEN ALPS AND APENNINES - THE CRITICAL TORINO HILL AND MONFERRATO AREA, NORTHWESTERN ITALY

The relationship between the Alpine and Apenninic orogenic systems is concealed at the surface by Tertiary sediments of two main tectonostratigraphic units: the 'Alpine-related' Torino Hill domain and the 'Apennines-related' Monferrato domain. Mapping and structural analyses carried out in the area behind the Mio-Pliocene Apenninic Padane thrust front allow comparison of the kinematic history of the Torino Hill and Monferrato domains. These are separate by the transpressive 'Rio Freddo Deformation Zone' (RFDZ), interpreted here as the superficial expression of a crustal discontinuity along which the Alpine metamorphic basement overrode the Apenninic Ligurian nappes during the Palaeogene.The Western Monferrato structural setting is the result of: (i) Late Oligocene-Burdigalian transpressive tectonics due to lateral displacement between the Alps-related and the Apennines-related domains; and (ii) compressive post-Messinian tectonics related to northward transport along the main Padane thrust front. Post-Messinian tectonic events affected also the NW-vergent asymmetrical Torino Hill anticline.