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 large-scale geological processes (e.g., crustal or mantle dynamics). 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 ca. 5 and 25 m Ma-1, with a factor of 2 difference between the western highland region and the central lowland region (13±6 m Ma-1 vs. 7±4 m Ma-1). Assuming a thin elastic plate model, the lithosphere flexural isostatic response to these denudation rates produces an overall uplift rate of the Armorican Peninsula from 4-8 m Ma-1 in the central lowland region and along the coast to 8-14 m Ma-1 in the western peninsula. We show that these erosion-driven uplift rates can explain the uplifted Late Pleistocene marine terraces along the Armorican Peninsula coastline and 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.