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

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Earth Surf. Dynam., 6, 257-270, 2018
https://doi.org/10.5194/esurf-6-257-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
29 Mar 2018
Extracting information on the spatial variability in erosion rate stored in detrital cooling age distributions in river sands
Jean Braun1,2, Lorenzo Gemignani3, and Peter van der Beek4 1Helmholtz Centre Potsdam, GFZ German Research Center for Geosciences, Potsdam, Germany
2Institute of Earth and Environmental Science, University of Potsdam, Potsdam, Germany
3Department of Earth Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, the Netherlands
4ISTerre, Université Grenoble Alpes, CS 40700, 38058 Grenoble CEDEX 9, France
Abstract. One of the main purposes of detrital thermochronology is to provide constraints on the 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. Other methods are based on an a priori knowledge of the in situ distribution of ages to interpret the detrital age distributions. In this paper, we describe a simple method that, using the observed detrital mineral age distributions collected along a river, allows us to extract information about the relative distribution of erosion rates in an eroding catchment without relying on a steady-state assumption, the value of thermal parameters or an a priori knowledge of in situ age distributions. The model is based on a relatively low number of parameters describing lithological variability among the various sub-catchments and their sizes and only uses the raw ages. The method we propose is tested against synthetic age distributions to demonstrate its accuracy and the optimum conditions for it use. In order to illustrate the method, we invert age distributions collected along the main trunk of the Tsangpo–Siang–Brahmaputra river system in the eastern Himalaya. From the inversion of the cooling age distributions we predict present-day erosion rates of the catchments along the Tsangpo–Siang–Brahmaputra river system, as well as some of its 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 method additionally allows comparing modern erosion rates to long-term exhumation rates. We provide a simple implementation of the method in Python 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., 6, 257-270, https://doi.org/10.5194/esurf-6-257-2018, 2018.
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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 contain information about the spatial distribution of the 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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