Local erosion rates versus active tectonics: cosmic ray exposure modelling in Provence (south-east France)

Lionel Siame (a), Olivier Bellier (b), Régis Braucher (b), Michel Sébrier (c), Marc Cushing (d), Didier Bourlès (b), Bruno Hamelin (b), Emmanuel Baroux (a), Beatrice de Voogd (e), Grant Raisbeck (f) and Françoise Yiou (f)

Earth and Planetary Science Letters
Volume 220, Issues 3-4 , 15 April 2004, Pages 345-364

Over the past decade, in situ-produced cosmogenic nuclides have revolutionised the study of landscape evolution. In particular, numerous studies have demonstrated that, in active tectonic settings, cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long-term deformation rates. In western European countries, erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates. In this study, we present the results of a depth-profiling technique applied to alluvial terraces located along the Rhône and the Moyenne Durance rivers. The expected decrease with depth of the measured 10Be concentrations has been modelled using a χ2 inversion method in order to constrain the exposure history of the alluvial sediments. The results suggest that: (1) over the Quaternary, the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m/Myr in southeastern France, and (2) providing a fairly good bracketing of the exposure age, the modelled abandonment age of alluvial terraces affected by the Moyenne Durance Fault allows estimating incision rates, comparing the alluvial terrace elevations with topographic river profiles, and a minimum vertical slip rate value of roughly 0.02 mm/yr for the southern segment of the Moyenne Durance Fault.

a Orsayterre, FRE 2566 CNRS, Bât. 504-2°, Université Paris-Sud, 91405, Orsay Cedex, France
b CEREGE (Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement), UMR CNRS 6635, Université Aix-Marseille III, P.O. Box 80, Europôle méditerranéen de l’Arbois, 13345, Aix-en-Provence Cedex 04, France
c Laboratoire de Tectonique, UMR CNRS 7072, Université Pierre et Marie Curie, T26-25, Case 129, 4, place Jussieu, 75252, Paris Cedex 05, France
d IRSN (Institut de Radioprotection de Sûreté Nucléaire), Bureau d’Evaluation des Risques Sismiques pour la Sûreté des Installations Nucléaires, P.O. Box 17, 92262, Fontenay-aux-roses Cedex, France
e Géologie et UMR5831, Laboratoire de Géophysique, avenue de l’Université, P.O. Box 1155, 64013, Pau Cedex, France
f Centre de Spectromérie Nucléaire et de Spectrométrie de Masse (IN2P3, CNRS), Bât. 108, Université Paris-Sud, 91405, Orsay Cedex, France