The uplift of the Adriatic flank of the Apennines since the Middle Pleistocene: New insights from the Tronto River basin and the Acquasanta Terme Travertine (central Italy)

Abstract

The Apennines chain is an active Neogene fold-and-thrust belt resulting from the westward subduction of the Adriatic microplate. Starting from the end of the Early Pleistocene, the chain was affected by an increase in regional uplift. Recent GPS data resolved uplift rates of 1–2 mm/yr for the whole Apennines, whereas, in the Adriatic flank, several studies estimated rates between 0.3 and 0.5 mm/yr over the last 1 Myr. A number of works investigated the evolution of the drainage systems along the Periadriatic margin of the Apennines providing long-term incision rates. Studies from the northern part of this sector reported uplift rates varying from 0.2 to 1.1 mm/yr, whereas only few studies concentrated on the central sector of the Adriatic flank of the Apennines, focusing mainly on the evolution of the lower reach of major rivers. This work aims to quantify the long-term rock uplift and incision rates of the eastern portion of the central Apennines through the analysis of the Tronto River basin. Because of its geologic and geomorphological configurations, this basin is an ideal test site to investigate the influence of tectonics and climate on the recent topographic evolution of the central Apennines. The basin extends, with a roughly WSW-ENE direction, from the inner sector of the chain to the Adriatic coast, crossing several tectonic structures such as the Amatrice extensional basin and the Acquasanta and Montagna dei Fiori anticlines. In particular, in the Acquasanta Terme area, the right flank of the Tronto River valley is characterized by fluvial and travertine deposits organized and exposed in several levels. In this work, we investigated the hydrography (river longitudinal profiles) and topography (swath profile, slope, and local relief) of the Tronto River basin coupling these data with field observations and geochronological analysis on the continental sediments (fluvial deposits and travertines) outcropping in the Acquasanta Terme area. To better characterize the nature of travertines, we performed geochemical characterization of three travertine-forming thermal springs obtaining their physico-chemical parameters, the percentage of dissolved gases, and the isotopes content. Finally, we applied a knickpoint celerity model to chronologically constrain the geomorphological evolution of the whole drainage system. The results show the occurrence of a continuous tectonic uplift (~0.5 mm/yr) across the study area since Middle Pleistocene. The uplift, together with climate fluctuations, drove the incision (~0.6 mm/yr) of the landscape and the delineation of the present drainage network. These data are consistent with previous estimates of uplift and incision rates in adjacent areas and provide new constraints on the Quaternary evolution of the central Apennines. This study highlights how the coupling of field surveys with morphometric and topographic analyses of a drainage system is crucial to understand and quantify the influence of tectonic and climate changes in shaping the landscape.