The Plio-Quaternary uplift of the Apennine Chain: new data from the analysis of topography and river valleys in Central Italy

Abstract

This study aimed at the reconstruction of magnitude and timing of uplift of a wide sector of the Central Apennines (Italy) by means of morphometric and morphostructural analyses. In the internal portion of the chain (where stratigraphic and geomorphological markers of past sea-level positions are lacking) the study was based on analysis of erosional landforms and river valleys. A large-scale topographic analysis was performed, processing 90-m and 230-m DEMs. The spatial distribution of several morphometric parameters, together with characteristic wavelengths of relief, allowed the distinction of three main regions affected by different cumulative surface uplift and tectonic/erosional fragmentation: a Peri-Tyrrhenian Belt; an Axial Belt; a Peri-Adriatic Belt. Particular attention was devoted to fluvial landforms, with analysis of longitudinal profiles and geometric pattern of the main stream-trunks and their relations with major structures. Major differences occur between the Tyrrhenian and Adriatic valley systems, the former being generally longitudinal and showing overall concave-upward longitudinal profiles, whereas the latter are generally transverse and possess less regular longitudinal profiles. Topographic features and river valleys architecture seem related to different styles and amounts of uplift in the three Belts. Within the study area, a narrower coast to coast transect (Gaeta-Vasto Transect, GVT) was investigated in detail, devoting particular attention to its axial sector, lying around the Apennines main divide (main divide area: MDA), and a possible scheme of the Quaternary surface uplift inside this transect was proposed. In the MDA, the main stages of landscape evolution and river network organization were reconstructed by analysis of paleosurfaces coupled with analysis of relic and present-day hydrographic network. This allowed recognition of a major phase of surface uplift (exceeding 1500 m in the Meta-Mainarde massif) occurred in response to thrusting during the Pliocene, whereas for the Quaternary uplift a minimum value around 400 m was estimated. Our study suggests that, during the Quaternary and in the GVT, the Peri-Tyrrhenian Belt suffered a subdued uplift operating over small wavelengths (10-15 km), while Axial and Peri- Adriatic Belts were subject to a stronger and long-wavelength (90 km) surface uplift, with maximum values (about 700 m) shifted NE of the Axial Belt and tapering to zero towards the Adriatic coast. The reconstructed pattern of uplift is coherent with the topographic properties of the three Belts and with the observed drainage features.