Catchment-averaged denudation rates derived from cosmogenic 10Be in the Northern Apennines (Italy) and implications for landscape dynamics

The Northern Apennines are an active orogenic wedge formed by subduction and rollback of the Adriatic plate over the last 30 Ma, where horizontal shortening and topographic advection lead to river capture and drainage divide migration. The orogen exhibits topographic asymmetry across the main drainage divide: the Adriatic side is steeper than the Ligurian side, suggesting drainage divide migration towards the Adriatic, opposite the direction of the horizontal tectonic advection of topography. In this study, we present new catchment-averaged denudation rates from major drainage basins in the Northern Apennines derived from cosmogenic ¹⁰Be concentrations, supplementing published data, in order to quantify the erosional fluxes from the orogen and compare the pattern of modern denudation rates with the topographic asymmetry. Catchment-averaged denudation rates and horizontal velocities increase from west to east throughout the study area; rates on the steeper Ligurian side of the main drainage divide are lower than those on the gentler Adriatic side. We reconcile these data with a kinematic model of slab rollback, where the erosional flux is described as a vector with horizontal and vertical components. The model predicts that the topography and denudation rates can be sustained by horizontal motion that dominates the Ligurian side, while both horizontal motion and vertical uplift are required on the Adriatic side. Our results help us assess how drainage divides evolve and provide insights into tectonically driven drainage reorganization, which may have important biodiversity implications, e.g., influencing the intraspecific genetic diversity of endemic riverine fish.