Late Pleistocene – Holocene denudation, uplift, and morphology evolution of the Armorican Massif (western Europe)

Abstract. Elevated Plio-Pleistocene coastal and marine markers in stable continental regions are commonly explained by a combination of eustatic sea-level variations and regional geodynamics (e.g., mantle dynamics, active faults). In this study, we test the role of erosion rates on the Late Pleistocene uplift and landform evolution of the Armorican Massif, western France. Denudation rates are estimated for 19 drainage basins using terrestrial cosmogenic nuclide (¹⁰Be) measurements in quartz. They range between 3 and 34 m.Ma^-1, with a factor of two difference between the western highland region and the central lowland region (16 ± 8 m.Ma^-1 vs. 9 ± 6 m.Ma^-1). Assuming a thin elastic plate model, the lithosphere flexural isostatic response to these denudation rates produces an overall uplift of the Armorican Peninsula from 12 – 15 m.Ma^-1 in the central lowland region to 4 – 10 m.Ma^-1 in the western peninsula and along the coastline. We show that these erosion-driven uplift rates can explain the uplifted Late Pleistocene marine terraces along the Armorican Peninsula coastline as well as the elevated Quaternary marine deposits in the central lowland region, without necessitating additional geodynamic processes such as regional compression or local active faults. Our results suggest that, in stable continental regions, long-term erosion should be taken into account as a driver of uplift and deformation before trying to derive global or regional geodynamic or tectonic conclusions.