The influence of mantle-lithosphere interaction on the evolution of relief formation and drainage networks

Remnants of the Variscan mountain belt can be found today throughout North America, North Africa, Europe, and Asia, which are typically characterized by hilly to mountainous topography. Since the topography of the Variscan orogen was already levelled in the Permian by post-orogenic erosion and thermal subsidence, processes independent of Variscan convergent tectonics must be responsible for the observed high topography. Central Europe encompasses several landscapes showing extensive post Variscan relief rejuvenation, including from west to east the Massif Central, the Vosges Mountains and Black Forest, and the Bohemian Massif. However, despite their spatial proximity, the underlying processes that led to uplift and relief rejuvenation could not be more different. For the Massif Central, mantle plume activity has been proposed, while continental rifting has been held responsible for uplift of the Black Forest and Vosges Mountains. Uplift of the Bohemian Massif has been attributed to the forebulge of the Alpine orogeny, or slab dynamics in the eastern Alps, respectively.

The aim of this study is to investigate the relationship between different uplift scenarios, relief formation and the response of the drainage system to spatial and temporal variations in uplift rates, focusing on the Massif Central, Black Forest and Vosges as well as the Bohemian Massif. The spatial and temporal succession of uplift rates as well as denudation rates in response to post orogenic uplift will be analysed based on an extensive compilation of low-temperature thermochronological data. Geomorphological analyses include the plan view and profile geometry of river networks, i.e., normalised steepness indices, across divide χ gradients and river orientation.

Although the underlying processes are different, relief rejuvenation is a striking feature in these mountain ranges. Low relief surfaces at higher elevations contrast with lower reaches, with deeply incised rivers and migrating knickpoints indicating temporal variations in uplift rates over the last millions of years. Furthermore, the organisation of river networks varies within the mountain ranges, highlighting the influence of underlying processes on the evolution of drainage networks. The Massif Central shows a radial, star-shaped drainage pattern with rivers steepening towards the centre of the plume related uplift. The Upper Rhine Graben is dominated by rift flank retreat governing drainage divide migration. This is expressed by short, steep rivers draining into the graben and long, low gradient rivers on the side facing away from the rift valley. The Bohemian Massif features a bowl-shaped topography, with tributaries of the Moldau (Vltava) draining north. However, the southern side of the Bohemian Massif drains into the Danube in short tributaries with steep lower reaches. These analyses in combination with thermochronometry pave towards constraining timing and spatial extent of the rejuvenation signal. Ultimately, this will allow for making inferences on the underlying driving mechanisms.