Morphometric evidences of topographic growth of the central Apennines

In active tectonic regions, topography results from the interaction between tectonics and surface processes. Geologic and geomorphic data suggest that the topographic growth of the Apennines was slow during the phase of crustal shortening (Miocene¡VPliocene), but accelerated in the Quaternary, when the tectonics was dominated by extension. Such disparate uplift rates should impart a unique fingerprint in the resulting landforms. We investigate the topography and the drainage features of a E-W transect across central Italy, focusing on topographic metrics, drainage pattern and stream long profiles. The results indicate that the Apennines topography is characterized by the superimposition of a short wavelength (20-30 km wide spacing), linked to local tectonic structures, and a long one that corresponds to a broad topographic bulge ƒî250 km wide, that records a regional uplift. As a response the rivers incised the topography of the growing chain mostly the same. In particular, on the Tyrrhenian side, the rectangular drainage pattern, and knickpoint in the long profiles suggest the strong influenced of the extensional tectonics. The rivers draining to the Adriatic Sea, that deeply incised gorges, show long profiles with knickpoints that correspond to rock changes. A high-resolution DEM of an area just south of Ancona provided information at a nested scale of observation. This region contains two major low relief surfaces. The highest one is located at the crest of the chain cutting across carbonates. The lower surface is inset into the flanks of the range and cut across turbidites. A third geomorphic surface, located more eastward, is underlain by Pliocene and Quaternary deposits. These geomorphic surfaces and distribution of the Pliocene deposits indicate that during slow emergence of the chain in the late Tertiary, surface processes shaped a low relief landscape that is preserved today as the summit surface. On the Adriatic side, the main trunks of the rivers progressively incised perpendicular to the compressive structures. Conversely, on the Tyrrhenian side, the influence of the active extension induced the formation of a rectangular network and locally internally-drained basins. Successively, during the Quaternary, the rivers, as a consequence of the ~250 km wide bulge uplift, deeply cut down the more emerged portions of the chain.