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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/esurf-2019-50
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-50
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Oct 2019

Submitted as: research article | 25 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Hillslope denudation and morphologic response across a rock uplift gradient

Vincent Godard1, Jean-Claude Hippolyte1, Edward Cushing2, Nicolas Espurt1, Jules Fleury1, Olivier Bellier1, Vincent Ollivier3, and ASTER Team1 Vincent Godard et al.
  • 1Aix-Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France
  • 2PSE-ENV/SCAN, Institut de Radioprotection et de Sûreté Nucléaire, Fontenay-aux-Roses, France
  • 3Aix-Marseille Univ, CNRS, Minist Culture, LAMPEA, Aix-en-Provence, France

Abstract. Documenting the spatial variability of tectonic processes from topography is routinely undertaken through the analysis of river profiles, as a direct relationship between fluvial gradient and rock uplift has been identified by incision models. Similarly, theoretical formulations of hillslope profiles predict a strong dependence on uplift rates. However, the reduced sensitivity of near-threshold hillslopes and the limited availability of high resolution topographic data, has often been a major limitation for their use to investigate tectonic gradients. Here we combined high resolution analysis of hillslope morphology and cosmogenic nuclides derived denudation rates to unravel the distribution of rock uplift across a blind thrust system at the Southwestern Alpine front in France. Our study is located in the Valensole Mio-Pliocene molassic basin, where a series of fold and thrust has deformed a plateau surface. We focused on a series of catchments aligned perpendicular to the main structures. Using a 1-m LiDAR Digital Terrain Model, we extracted hillslopes topographic properties such as hilltop curvature CHT or non-dimensional erosion rates E*. We observed a systematic variation of these metrics coincident with the location of a major underlying thrust system identified by seismic surveys. Using a simple deformation model, the inversion of the E* pattern allows to propose a location and dip for a blind thrust, which are consistent with available geological and geophysical data. We also sampled clasts from eroding conglomerate at several hilltops locations for 10Be and 26Al concentration measurement. Calculated hilltops denudation rates range from 40 to 120 mm/ka. These denudation rates appear to be correlated with E* and CHT extracted from the morphological analysis, and are used to derive absolute estimates for the fault slip rate. This high resolution hillslope analysis allows to resolve short wavelength variations in rock uplift, that would not be possible to unravel using commonly used channel profiles based methods. Our joint analysis of topography and geochronological data supports active thrusting at the Southwestern alpine front, and such approaches may bring crucial complementary constraints to morphotectonic analysis for slip rates on slow active faults.

Vincent Godard et al.
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