3D Structure Of The Northern Marche Region, And Implications For The Active Tectonics Of The Outer Northern Apennines (Italy)

F. Borraccini, M. De Donatis, S. Mazzoli, and D. Savelli

The quaternary tectonics of the northern Marche sector of the outer Northern Apennines has been analysed. Late Miocene – Pliocene orogenic structures include mainly NE verging thrusts and associated folds whose geometry is locally controlled by slip on oblique and lateral ramp segments. Post-orogenic features consist mainly of roughly N-S trending normal faults and NE-SW striking, oblique-slip transfer faults with a left-lateral component of motion, resulting from WSW-ENE oriented extension. These faults, also affecting late-Quaternary continental deposits, hint at a recent tectonic behaviour congruent with the geomorphologic evolution of the study area. On the other hand, available focal mechanisms indicate a dominant NNW-SSE oriented compression, not compatible with NE directed thrusting. The inactivity of the thrust front off-shore is also well documented by the interpretation of seismic lines calibrated with borehole data, which points out that middle-upper Pleistocene siliciclastic deposits seal the orogenic features. On land, fluvial terraces maintain their overall parallelism even across the anticline ridges, hinting at a generalised vertical uplift, and disclaiming significant deformation by the growth of NW-SE trending folds ever since the latest mid-Pleistocene. Within this framework, active NNW-SSE oriented compression could be responsible for the reactivation of suitably oriented segments of pre-existing blind thrust faults (i.e. E-W to NE-SW striking oblique/lateral ramps), that in turn could control the evolutions of ENE-WSW trending sectors characterised by differential uplift.