From spatio-temporal patterns of river incision rates to Quaternary uplift history of the Variscan Rhenish/Ardenne Massif (N. Europe)

The Rhenish/Ardenne Massif (RAM) is one the most “emblematic” Variscan structures located north of the Alps. Intraplate uplift affected the RAM during the Plio-Quaternary along with other Palaeozoic massifs located in the alpine foreland. However, its cause(s), shape and rates are still poorly understood and therefore remain debated. This was, until recently, mainly due to a lack of reliable ages for uplift markers, such as the Quaternary terrace staircases along deeply incised valleys of the Rhine, Moselle and Meuse as well as their main intra-massif tributaries. Several studies based on numerical dating methods (i.e., cosmogenic nuclides, ESR, OSL…) have shed new light on these questions by assigning numerical age estimates on key levels of fluvial terraces or cave levels related to phases of regional base-level stability.

This contribution compiles all chronological data produced over the last twenty years. Plio-Quaternary incision rates are accordingly reconstructed. A similar trend is reported throughout the RAM with a peak of incision occurring during the Early or Middle Pleistocene and matching the main massif-wide geomorphological marker. However, age control reveals a significant time lag (>250 ka) between the south-eastern and north-western RAM margins. High incision rates onset is consistently older along the Rhine/Moselle and tributaries than along the Meuse and tributaries. This key finding is well in line with the hypothesis arguing for a wave of uplift migrating northward throughout the RAM. It also supports regional tectonic causes for uplift (i.e., upper-crustal stress transfer from the Alps to their foreland) rather than more local ones.