10Be-inferred paleo-denudation rates imply that the mid-Miocene western central Andes eroded as slowly as today

Madella, Andrea; Delunel, Romain; Akçar, Naki; Schlunegger, Fritz; Christl, Marcus (2018). 10Be-inferred paleo-denudation rates imply that the mid-Miocene western central Andes eroded as slowly as today. Scientific Reports, 8(1), p. 2299. Nature Publishing Group 10.1038/s41598-018-20681-x

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Terrestrial cosmogenic nuclide concentrations of detrital minerals yield catchment-wide rates at which hillslopes erode. These estimates are commonly used to infer millennial scale denudation patterns and to identify the main controls on mass-balance and landscape evolution at orogenic scale. The same approach can be applied to minerals preserved in stratigraphic records of rivers, although extracting reliable paleo-denudation rates from Ma-old archives can be limited by the target nuclide’s half-life and by exposure to cosmic radiations after deposition. Slowly eroding landscapes, however, are characterized by the highest cosmogenic radionuclide concentrations; a condition that potentially allows pushing the method’s limits further back in time, provided that independent constraints on the geological evolution are available. Here, we report 13–10 million-year-old paleo-denudation rates from northernmost Chile, the oldest 10Be-inferred rates ever reported. We find that at 13–10 Ma the western Andean Altiplano has been eroding at 1–10 m/Ma, consistent with modern paces in the same setting, and it experienced a period with rates above 10 m/Ma at ~11 Ma. We suggest that the background tectono-geomorphic state of the western margin of the Altiplano has remained stable since the mid- Miocene, whereas intensified runoff since ~11 Ma might explain the transient increase in denudation.

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