Old orogens – young topography
PIs: Fabian Dremel, Christoph v.Hagke, Jörg Robl, Bjarne Friedrichs
The Variscan orogeny lasted from the Late Devonian to the Early Permian and resulted in a mountain range whose remnants can be found today in North America, Northern Africa, Europe and Asia. Although the mountain range was almost completely eroded to peneplains in the Permian, today the Variscan massifs (e.g., Appalachians, Massif Central, Black Forest-Vosges, Bohemian Massif) feature hilly to mountainous topography with peak elevations exceeding 1500 metres. These mountain ranges are characterised by low relief surfaces, rounded hilltops and graded river profiles with low channel gradients at higher elevations, but deeply incised rivers with migrating knickpoints and steep valley flanks prone to mass wasting at lower elevations near the base level of the receiving streams. This landscape bimodality may indicate temporal and/or spatial variations in uplift rates during the last million years. Clearly, the latest surface uplift is unrelated to the original mountain building phase, but cause, wavelength, timing and rates are still disputed.
The studied Variscan massifs include the Massif Central, the Black Forest-Vosges, the Rhenish Massif and the Bohemian Massif. Despite the spatial proximity of these four mountain ranges within Central Europe, the underlying processes that led to uplift and relief rejuvenation since the Eocene could not be more different. Whereas the Massif Central and parts of the Rhenish Massif are dominated by mantle plume activity, the emergence of the present Bohemian Massif and the Black Forest-Vosges is strongly coupled with the Alpine orogeny. Although the underlying processes were already explored, the temporal and spatial succession of the signals is not fully understood. This is however needed for a more complete understanding of the processes themselves. In the context of this PhD project, I intend to quantify the influence of mantle related processes on post-orogenic landscape evolution. First and foremost, I want to test the following hypotheses:
- Mantle related processes are a driving factor for relief rejuvenation in non-collisional, post-orogenic landscape
- Mantle processes lead to the evolution of characteristic landscape features, with a characteristic imprint on the drainage patterns and drainage organisation
To achieve this goal, I will use a combination of geomorphic analyses, low-temperature thermochronology, and numerical landscape evolution models to investigate relief rejuvenation. Using these methods, landscape dynamics can be constrained on different timescales, with geomorphic analyses as well as thermochronology covering the post-orogenic period. Landscape evolution models will be used to bridge the scales and bring the first two approaches together into conceptual models regarding relief rejuvenation. This project aims at constraining the underlying factors of relief rejuvenation within Variscan massifs by (a) quantifying the spatial occurrence of disequilibrium landscape features with geomorphic analyses, (b) determining the rate of rock uplift and denudation through low-temperature thermochronometry and (c) constraining the causes of rock uplift within these non-collisional mountain ranges by amalgamating the first two approaches supported using the numerical landscape evolution model OpenLEM and thermal history modelling.
Figure 1: ksn maps for the selected study sites
Figure 2: Compilation of existing AFT and apatite U-Th/He ages; grey lines: dominant faults; triangles: AFT, hexagons: apatite U-Th/He