Modelling Pliocene-Quaternary landscape evolution recorded by low-temperature thermochronology in the glacially overprinted Tauern Window, Eastern European Alps

The topography of mountain belts results from complex variations and interactions between tectonic, climatic and erosional processes. In particular, glaciations result in heterogenous incision along and across mountain valleys. The European Alps have been periodically extensively glaciated since the late Pliocene-Quaternary; however, the impact of these glaciations on the evolution of both orogen-scale and valley-scale relief development and erosion remains disputed. One reason for that is the lack of temporal resolution on timescales of 10⁵ to 10⁶ years.

The low-temperature apatite (U-Th)/He (AHe) thermochronometric system is sensitive to the past shape of the near-surface 65 to 85 °C isotherm, which, at a corresponding depth of ∼2 to 4 km below the surface, follows the approximate shape of the landscape at the time. This feature allows deriving the evolution of topography following the time that rock samples cooled through the isotherm. Thus, provided a well understood tectonic rock-uplift history and suitably distributed ages covering the Pliocene-Quaternary period, AHe data can be used to model the glacial impact on mountain morphology.

The Tauern Window in the Eastern European Alps presents an ideal natural laboratory for this approach, as (1) its rapid tectonically driven exhumation until ~8 Ma is well documented in literature, and (2) there is clear glacial overprinting and relatively high relief within its valleys. Here, we present four new AHe elevation profiles along valleys of differing sizes and orientations in the Western Tauern Window, with AHe ages ranging from ~1.4 to 18.2 Ma.

AHe ages generally increase with elevation, with a prominent and rapid Pliocene-Quaternary exhumation signal recorded in the thermal histories of the valley bottom samples only. We interpret this to signify that regional tectonics alone cannot explain the full exhumation history of the region. We further test this hypothesis, using 3D thermo-kinematic inverse modelling in PecubeGUI to quantify the timing and amount of focused glacial valley deepening.  These models are also used to predict the youngest thermal history information, or “edge age”, that we can expect when using the higher-resolution apatite ⁴He/³He methodology in this area in the future.