THE PLIO-QUATERNARY UPLIFT OF THE APENNINE CHAIN: NEW DATA FROM THE ANALYSIS OF TOPOGRAPHY AND RIVER VALLEYS IN CENTRAL ITALY

This study aims at the reconstruction of magnitude and timing of surface uplift affecting a wide sector of the Central Apennines (Italy) by means of morphometric and morphostructural analyses. In the chain interiors (where stratigraphic and geomorphological markers of past sea-level positions are lacking) the study is based on analysis of erosional landforms and river valleys. A large-scale topographic analysis, by processing 90-m and 230-m DEMs, is performed. The spatial distribution of several morphometric parameters, together with characteristic wavelengths of relief, allowed the differentiation of three main regions affected by different cumulative surface uplift and tectonic/erosional fragmentation: a Peri-Tyrrhenian Belt, an Axial Belt and a Peri-Adriatic Belt. Particular attention is devoted to fluvial landforms, with analysis of longitudinal profiles and geometric pattern of the main drainage lines and their relations with the major structures. Major differences occur between the Tyrrhenian and Adriatic valley systems. The Tyrrhenian drainage mainly consists of longitudinal valleys displaying overall concave-up longitudinal profiles. The Adriatic drainage is mainly constituted by transverse streams and shows less regular longitudinal profiles. Topographic features and the river valley architecture seem related to different styles and amounts of uplift in the three belts. Within the study area, a coast to coast transect (Gaeta-Vasto Transect, GVT) has been investigated in detail, focusing the analysis on its axial sector, around the Apennines main divide (Main Divide Area,MDA). A possible scheme of Quaternary surface uplift along the GVT is proposed. In the MDA, the main stages of landscape evolution and drainage organization can be reconstructed by means of the analysis of paleosurfaces coupled with study of the relict and present-day drainage networks. This allowed the recognition of a major phase of surface uplift (exceeding 1500 m in the Meta-Mainarde massif) that occurred in response to thrusting during the Pliocene. For Quaternary surface uplift a minimum value of 400 m can be estimated. This study suggests that, during the Quaternary, the Peri-Tyrrhenian Belt suffered a subdued uplift acting over small wavelengths (10–15 km), while the Axial and Peri-Adriatic Belts were subject to a larger and longwavelength (90 km) surface uplift, with maximum values (about 700m) shifted to the 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.