Abstract

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.