Quantifying Glacial Erosion in the European Alps with Thermochronological Age Distributions

Abstract:

Low temperature thermochronology is a widely used tool to quantify long-term exhumation rates and decipher landscape evolution. In this study we use the spatial variations in apatite fission track (AFT) ages along major valleys to investigate the impact of Quaternary glacial erosion in the European Alps.

To analyze the influence of glacial erosion on the thermochronological age distribution, we chose a study area in the Central Alps of Switzerland, which was strongly affected by Quaternary glaciations. Additionally, this area provides already published AFT ages and combined with our samples, we have a relatively high spatial sample density.

The major uplift phase of the Alpine orogeny occurred in Miocene, whereas nowadays active tectonics in the Central Alps of Switzerland is below the limit of detection. However, our results reveal a non-uniform AFT age-elevation trend and as these can not be easily linked to active tectonics, instead glacial erosion may be the driving mechanism. The AFT ages of bedrocks vary between ~4 Ma and ~12 Ma, resulting in an average exhumation rate of ~0.5 km/Ma for the last ~8 Ma. The age-elevation relation follows a distinct local trend along major valleys, whereby the youngest ages are not found at the lowest point. We suggest that the AFT age distribution is a result of spatially non-uniform (glacial) erosion. A simple 3D thermal-kinematic modelling with Pecube confirms the assumption, as spatially uniform exhumation can not explain this age-elevation trend. We propose that focused valley incisions occurred during Quaternary glaciations, which led to distinct thermochronological age distributions along major valleys.