Cover thrust reactivations related to internal basement involvement during Neogene‐Quaternary evolution of the northern Apennines

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Abstract
Up to recently the Neogene‐Quaternary evolution of the northern Apennines (Italy) has been described by the classic model of a migrating eastward, compressive external front, with an extensional regime in the back areas connected with the Tyrrhenian basin formation. However, in the last few years, new structural data have been collected in the internal marine and continental episutural basins, and in the external exposed thrust belt. A complex structural evolution has now been reconstructed, with coeval main tectonic phases that affect both areas with stress field change. Four main tectonic phases have been identified since Late Tortonian times; these are dated as Messinian, late Pliocene, middle, and late Pleistocene. The thrust belt has a complex evolution, detected in a wide external area of the chain after the first emplacement of the main thrust sheets, with reactivations and out of sequence thrusting. These reactivation phases fit very well with the compressive phases affecting the sediments of the internal basins, suggesting a direct relationship within a single evolutive model. The increased knowledge of the deep structure of the northern Apennines through geophysical and subsurface data acquired in the last few years indicates the basement involvement at least for the internal side of the northern Apennines. This basement involvement also played an important role in the tectonic evolution of the external sector of the Apennines. In this paper a new model is proposed that integrates field data, geophysical evidence, and geodynamic constraints. The thrust reactivations and the out‐of‐sequence structures of the external area are related to internal crustal thrust activity. The deformed sediments of the Neogene‐Quaternary basins are dating the thrust activity. All the evidences point to a late Neogene rejuvenation of the tectonic evolution, but some inferences can be drawn on the development of the foredeep.