ESR-thermochronometry in the western European Alps (Switzerland)

The western European Alps are characterised by deeply incised valleys, however the timing of their formation and the impact of Quaternary glaciation on rates of erosion remains disputed. This is mainly due to a lack of geochronological methods that cover the timespan of 103-106 years. Electron spin resonance (ESR) thermochronometry has a high potential to fill this temporal gap because of its low closure temperature (<100 C), potentially allowing changes in erosion rates to be related to glacial advance and retreat. The Rhne Valley (Switzerland) was intensively glaciated during the Quaternary 1 while it is unclear how tributary valleys incised throughout the glaciation period. In this study, we focus on two study sites along the main valley, close to Sion and Visp and the Matter and Vispa river tributary valleys, towards Zermatt and Saas-Fee to compare their Quaternary exhumation histories. Whilst bedrock samples from Sion yielded cooling ages between 209 and 674 ka, samples from Visp showed saturation around 2500 ka. Thermal stability varied between samples and signals, and sample measurement is ongoing. Preliminary inversion of the data shows that the low closure temperatures of the ESR signals in quartz allow the Late Quaternary exhumation of the Alpine valleys to be resolved, providing new insights into the glacial incision history during the Quaternary and especially how erosion rates varied temporally under a changing climate. Reference: 1 Valla, P.G., D.L. Shuster, and P.A. van der Beek. 2011. Significant increase in relief of the European Alps during mid-Pleistocene glaciations, Nature Geoscience. 4(10): p. 688-692.