Late Neogene exhumation and relief development of the Aar and Aiguilles Rouges massifs (Swiss Alps) from low-temperature thermochronology modeling and 4He/3He thermochronometry

The late Neogene-Quaternary exhumation history of the European Alps is the subject of controversial findings and interpretations, with several thermochronological studies arguing for long-term steady state exhumation rates, while others have pointed to late Miocene-Pliocene exhumation pulses associated with tectonic and/or climatic changes. Here, we perform inverse thermal-kinematic modeling on dense thermochronological data sets combining apatite fission track (AFT) data from the literature and recently published apatite (U-Th-Sm)/He (AHe) data along the upper Rhone valley (Aar and Aiguilles Rouges massifs, Swiss Alps) in order to derive precise estimates on the denudation and relief history of this region. We then apply forward numerical modeling to interpret cooling paths quantified from apatite He-4/He-3 thermochronometry, in terms of denudation and relief-development scenarios. Our modeling results highlight the respective benefits of using AFT/AHe thermochronology data and He-4/He-3 thermochronometry for extracting quantitative denudation and relief information. Modeling results suggest a late Miocene exhumation pulse lasting until similar to 8-10 Ma, consistent with recently proposed exhumation histories for other parts of the European Alps, followed by moderate (similar to 0.3-0.5 km Myr(-1)) denudation rates during the late Miocene/Pliocene. Both inverse modeling and He-4/He-3 data reveal that the late stage exhumation of the studied massifs can be explained by a significant increase (similar to 85-100%) in local topographic relief through efficient glacial valley carving. Modeling results quantitatively constrain Rhone valley carving to 1-1.5 km since similar to 1 Ma. We postulate that recent relief development within this part of the Swiss Alps is climatically driven by the onset of major Alpine glaciations at the mid-Pleistocene climate transition.