Hillslope denudation and morphologic response to a rock uplift gradient
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Published:2020-04-07
Issue:2
Volume:8
Page:221-243
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ISSN:2196-632X
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Container-title:Earth Surface Dynamics
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language:en
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Short-container-title:Earth Surf. Dynam.
Author:
Godard VincentORCID, Hippolyte Jean-ClaudeORCID, Cushing EdwardORCID, Espurt Nicolas, Fleury Jules, Bellier Olivier, Ollivier VincentORCID,
Abstract
Abstract. Documenting the spatial variability of tectonic processes from topography is routinely undertaken through the analysis of river profiles, since
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 their base-level lowering rate, which in most situations is set by channel incision. 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-nuclide-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 Mio-Pliocene Valensole molassic basin, where a series of folds and thrusts 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 hillslope topographic properties
such as hilltop curvature CHT and nondimensional erosion rates E∗.
We observed 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 us 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 conglomerates at several hilltop locations for 10Be and 26Al concentration measurements. Calculated hilltop
denudation rates range from 40 to 120 mm kyr−1. These denudation rates appear to be correlated with E∗ and CHT that were extracted
from the morphological analysis, and these rates are used to derive absolute estimates for the fault slip rate. This high-resolution hillslope analysis allows
us to resolve short-wavelength variations in rock uplift that would not be possible to unravel using commonly used channel-profile-based
methods. Our joint analysis of topography and geochronological data supports the interpretation of active thrusting at the southwestern Alpine
front, and such approaches may bring crucial complementary constraints to morphotectonic analysis for the study of slowly slipping faults.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Geophysics
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