COMPRESSIVE NEOGENE‐QUATERNARY TECTONICS IN THE HINTERLAND AREA OF THE NORTHERN APENNINES

Abstract

The NW‐SE trending Northern Apennine Mountains consist of a series of allochthonous units which were thrust generally to the NE during Neogene crustal shortening, in the direction of a foreland basin to the east andNE. On the hinterland (internal) side of this fold‐and‐thrust belt, a series of small‐scale sedimentary basins developed from the late Miocene and were deformed at the same time. The late Tortonian‐Pleistocene evolution of the Northern Apennines has previously been considered by most authors in terms of a classical model of a NE‐migrating compressional front, which was followed in time and space by a hinterland extensional regime related to the development of the Tyrrhenian Basin.This paper presents new structural data from both the external parts of the Northern Apennines and the late Tortonian‐Pleistocene basins located in the internal sector. In the Northern Apennine thrust belt, reactivation and out‐of‐sequence geometries for the thrust faults have been recorded. In the hinterland basins, compressional deformation has been documented and is usually associated with thrust ramps and regional unconformities. The timing of both thrust reactivation and of the major compressional phases affecting the hinterland basins is closely correlated with periods of magmatic quiescence, and with compressional phases detected in the external margin of the Northern Apennines (the Padan‐Adriatic foredeep).Data presented in this paper indicate that compressional deformation has played a major role in the recent evolution of the Northern Apennines. The mechanism envisaged to explain this tectonic framework takes account of the piggy‐back emplacement of basement thrusts from internal to external sectors, which occurred in post‐Serravallian time. Activity on basement thrusts may have caused reactivation of thrusts in the internal cover sequence, giving rise to out‐of‐sequence geometries and controlling the development and/or deformation of the hinterland basins. This type of structural evolution has resulted in a complex geometry for the thrust sheets, and this must be taken into consideration during re‐interpretation of the structure of the Northern Apennines. It may also have important implications for petroleum exploration.