COVER THRUST REACTIVATIONS RELATED TO INTERNAL BASEMENT INVOLVEMENT DURING NEOGENE-QUATERNARY EVOLUTION OF THE NORTHERN APENNINES

Up to recently the Neogene-Quatemary evolution of the northern Apennin es (Italy) has been described by the classic model of a migrating east ward, compressive external front, with an extensional regime in the ba ck areas connected with the Tyrrhenian basin formation. However, in th e last few years, new structural data have been collected in the inter nal marine and continental episutural basins, and in the external expo sed thrust belt. A complex structural evolution has now been reconstru cted, with coeval main tectonic phases that affect both areas with str ess field change. Four main tectonic phases have been identified since Late Tortonian times; these are dated as Messinian, late Pliocene, mi ddle, and late Pleistocene. The thrust belt has a complex evolution, d etected in a wide external area of the chain after the first emplaceme nt of the main thrust sheets, with reactivations and out of sequence t hrusting. These reactivation phases fit very well with the compressive phases affecting the sediments of the internal basins, suggesting a d irect relationship within a single evolutive model. The increased know ledge of the deep structure of the northern Apennines through geophysi cal and subsurface data acquired in the last few years indicates the b asement involvement at least for the internal side of the northern Ape nnines. This basement involvement also played an important role in the tectonic evolution of the external sector of the Apennines. In this p aper a new model is proposed that integrates field data, geophysical e vidence, and geodynamic constraints. The thrust reactivations and the out-of-sequence structures of the external area are related to interna l crustal thrust activity. The deformed sediments of the Neogene-Quate rnary basins are dating the thrust activity. All the evidences point t o a late Neogene rejuvenation of the tectonic evolution, but some infe rences can be drawn on the development of the foredeep.