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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/esurf-2017-42
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
13 Jul 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).
Extracting information on the spatial variability in erosion rate stored in detrital cooling age distributions in river sands
Jean Braun1, Lorenzo Gemignani2, and Peter van der Beek3 1GFZ German Research Centre for Geosciences, Telegrafenberg 14473, Potsdam, Germany
2Department of Earth Sciences, Cluster Geology and Geochemistry, Vrij Universiteit Amsterdam, the Netherlands
3ISTerre, Université Grenoble Alpes and CNRS, CS 40700, 38058 Grenoble CEDEX 9, France
Abstract. The purpose of detrital thermochronology is to provide constraints on regional scale exhumation rate and its spatial variability in actively eroding mountain ranges. Procedures that use cooling age distributions coupled with hypsometry and thermal models have been developed in order to extract quantitative estimates of erosion rate and its spatial distribution, assuming steady state between tectonic uplift and erosion. This hypothesis precludes the use of these procedures to assess the likely transient response of mountain belts to changes in tectonic or climatic forcing. In this paper, we describe a simple method that, using the observed detrital mineral age distributions collected in a system of river catchments, allows to extract information about the relative distribution of erosion rates in an eroding hinterland without relying on a steady-state assumption or the value of thermal parameters. The model is based on a relatively low number of parameters describing lithological variability among the various catchments and their sizes, and only uses the raw binned ages. In order to illustrate the method, we invert age distributions collected in the Eastern Himalaya, one of the most tectonically active places on Earth. From the inversion of the cooling age distributions we predict present day erosion rates of the catchments along the Siang-Tsangpo-Brahmaputra river system, as well as smaller tributaries. We show that detrital age distributions contain dual information about present-day erosion rate, i.e. from the predicted distribution of surface ages within each catchment and from the relative contribution of any given catchment to the river distribution. The inversion additionally allows comparing modern erosion rates to long-term exhumation rates. We provide a simple implementation of the method in R.code within a Jupyter Notebook that includes the data used in this paper for illustration purposes.

Citation: Braun, J., Gemignani, L., and van der Beek, P.: Extracting information on the spatial variability in erosion rate stored in detrital cooling age distributions in river sands, Earth Surf. Dynam. Discuss., https://doi.org/10.5194/esurf-2017-42, in review, 2017.
Jean Braun et al.
Jean Braun et al.

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Short summary
We present a new method to interpret a type of data that geologists obtained by dating minerals in river sand samples. We show that such data contains information about the spatial distribution of erosion rate (wear of surface rocks by natural processes such as river incision, land sliding or weathering) in the regions neighboring the river. This is important to understand the nature and efficiency of the processes responsible for surface erosion in mountain belts.
We present a new method to interpret a type of data that geologists obtained by dating minerals...
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