Interactions between mantle upwelling, drainage evolution and active normal faulting: an example from the central Apennines (Italy)

In this paper we show that the processes that have shaped the Quaternary su rface development of the Apennines in central Italy are all consequences of a single subcrustal process, the upwelling of the mantle. The relationship between gravity and topography shows that mantle convection is responsible for a long-wavelength (150-200 km) topographic bulge over the central Apen nines, and stratigraphic evidence suggests this bulge developed in the Quat ernary. Active normal faulting is localized at the crest of this bulge and produces internally-draining fault-bounded basins. These basins have been p rogressively captured by the aggressive headward erosion of major streams t hat cut down to the sea on the flanks of the regional bulge. The only survi ving closed basins are those on the Apennine watershed most distant from th e marine base level, where continued normal faulting is still able to provi de local subsidence that defeats their capture by the regional drainage net work. Understanding the competition between regional capture and local, fau lt-related subsidence of intermontane basins is crucial for recognizing pot entially hazardous active faults in the landscape and also for interpreting the sediment supply to adjacent offshore regions. Central Italy provides a good modern analogue for processes that are probably common in the geologi cal record, particularly on rifted margins and intracontinental rifts, but may not have been fully appreciated.