Uplift, erosion, and advection within the orogenic wedge of the Northern Apennines (Italy)

Abstract

The Northern Apennines are an active orogenic wedge formed by subduction and rollback of the Adriatic slab over the last 30 Ma, with high rates of horizontal tectonic advection of topography from northeast to southwest. The orogen exhibits topographic asymmetry across the main drainage divide: the retrowedge on the Ligurian (generally southwestern) side is steeper than the prowedge on the Adriatic (generally northeastern) side. In this study, we present new catchment-averaged erosion rates and horizontal velocities from major drainage basins in the northwestern 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 erosion rates with the topographic asymmetry. Catchment-averaged erosion 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 erosion 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 provide insights into tectonically driven drainage reorganization, where horizontal shortening and topographic advection lead to river capture and drainage divide migration opposite the direction of the horizontal tectonic advection of topography.