Incised relict landscapes in the eastern Alps.

We investigate landscape evolution in a region of the Alps that has escaped glacial erosion during periodic glaciations of the last million years. The research is thus suited to investigate landscaping processes on a longer time scale at the eastern end of the Alps. Morphometric analysis reveals the presence of incised relict landscapes in several regions. In the Koralpe range topographic analysis is interpreted in terms of the relict landscape being present on both sides of the eastward tilted Koralpe block. This suggests that the relict landscape is younger than the tilting of the range, which is inferred to have taken place between 18 and 16Ma. In the Pohorje region, a relict landscape is developed across the contacts of a 19Ma pluton. We use apatite (U-Th)/He thermochronology to constrain the possible age of the Koralpe and Pohorje relict landscapes. The results indicate that the Pohorje massif had cooled below 70°C by about 15Ma suggesting that the relict landscape must be younger -- consistent with the interpretation of the Koralpe range. These results suggest that many relict landscapes of the eastern Alps may have formed after 15Ma in a period of tectonic quiescence and erosion. However, in both ranges channel profile projections show that about 387±105m uplift and incision occurred subsequently. This incision is likely to have occurred during the last 6-5Ma in response to the uplift of the whole region. It testifies to a renewed and ongoing uplift event that is earlier than the glaciation periods but might easily be confused with impact of glacial erosion elsewhere in the eastern Alps. [ABSTRACT FROM AUTHOR]