Cosmogenic ³He and ¹⁰Be denudation rates in the Central Andes: Comparison with a natural sediment trap over the last 18 ka

Swann Zerathe (1) , Camille Litty (1) , Pierre-Henri Blard (2) , Fabrizio Delgado (1) , Laurence Audin (1) , Julien Carcaillet (1) , Team Aster (3)

1 ISTerre - Institut des Sciences de la Terre
2 CRPG - Centre de Recherches Pétrographiques et Géochimiques
3 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

It is of major importance for Earth surface sciences to reconstruct denudation rates in the most precise and accurate way. For this, it can be useful to test on the same setting methods based on different assumptions, such as those relying on geomorphological and geochemical observations. Here, we use an exceptionally suited setting in the Locumba catchment (southwestern Peruvian Andes) that offers the unique opportunity to compare denudation rates derived from in situ cosmogenic ³He and ¹⁰Be with a geomorphological sediment budget integrated over the last 18 ka. The sediment budget is estimated by determining the volume of sediment trapped in the Aricota lake that formed 18 ka ago after the occurrence of a giant rockslide dam. We reconstructed the topography of the Locumba valley before the dam emplacement and established that the captured sediment volume is 0.8 ± 0.1 km³. Considering that the lake-water output is restricted to seepage through the dam and that overflow above the dam never occurred, this volume correctly represents the sediment flux integrated over the last 18 ka. Integrating this volume over the upstream catchment area (∼1500 km²), we derived a corresponding mean erosion rate of 30 ± 9 mm.ka^-1. Fluvial sediments feeding the Aricota lake were sampled to derive denudation rates from in-situ cosmogenic ¹⁰Be in the silicates and from in-situ cosmogenic ³He in the ferromagnesian minerals. Cosmogenic nuclide denudation rates from the main stream are 30 ± 2, 33 ± 2, 21 ± 1 and 82 ± 5 mm.ka^-1 for the ¹⁰Be-quartz, the ¹⁰Be-feldspar, the ³He-amphibole and ³He-pyroxene, respectively. The consistency between the cosmogenic nuclide denudation rates derived from ¹⁰Be in the silicates and the erosion rate derived from our sediment budget shows that the ¹⁰Be accurately estimates of the sediment flux. Additionally, this work provides the first successful application of ¹⁰Be-feldspar nuclide-mineral pair to derive catchment-mean denudation rate and demonstrate that ¹⁰Be-feldspar can thus be a good alternative in catchments dominated by volcanic rocks with no quartz. The discrepancies observed between the denudation rates derived from the ³He-amphibole and ³He-pyroxene couples require further studies.

Mots clés: cosmogenic nuclide; denudation rate; <SUP>10</SUP>Be and <SUP>3</SUP>He; multiple-minerals; sediment budget; Central Western Andes

Domaines: Planète et Univers [physics]; Sciences de la Terre

Swann Zerathe, Camille Litty, Pierre-Henri Blard, Fabrizio Delgado, Laurence Audin, et al.. Cosmogenic ³He and ¹⁰Be denudation rates in the Central Andes: Comparison with a natural sediment trap over the last 18 ka. Earth and Planetary Science Letters, 2022, 599, ⟨10.1016/j.epsl.2022.117869⟩. ⟨insu-03851898⟩