Accelerated uplift of the Rhenish Massif (central Europe) since 700–800 ka revealed by isochron-burial dating of strath terraces

The uplift of the Rhenish Massif is recorded by strath terraces along major rivers, however, absolute age control for the terraces is still scarce, and terrace correlations with Quaternary climate cycles are uncertain and partly contradictory. Along the Rhine, two terrace levels – the Older and Younger Main Terrace (OMT and YMT) – occur above a marked break-in-slope, which separates a steep lower valley from a broad upper valley with gentle slopes. Based on limited paleomagnetic data, an age of 730–800 ka for the YMT was often assumed and used to estimate rock uplift (e.g., Meyer & Stets, 1998). Here, we present the first ¹⁰Be – ²⁶Al isochron-burial ages for the OMT and YMT at two sites: Kasbach-Ohlenberg and Bad Hönningen. At Kasbach-Ohlenberg, the OMT yields a burial age of 1.4–1.6 Ma, while the YMT is dated to 0.7–0.8 Ma. These ages and the small vertical distance of only a few meters between both terraces indicate a prolonged period with little river incision, followed by a phase of more rapid incision and rock uplift. The elevation of the bedrock strath of the YMT above the Rhine (i.e., ~160 m) implies an average uplift rate of ~200 m/Ma during this phase. At Bad Hönningen, the OMT yields a burial age of 1.1-1.4 Ma. This younger age and the higher elevation of the OMT at this site suggest that rock uplift increases toward the internal part of the Rhenish Massif. The temporal coincidence between the onset of uplift and plume-related intraplate volcanism in the Eifel at ~700 ka (e.g., Lippolt et al., 1983) suggests a mantle-driven origin for the uplift. Our ongoing work will result in additional age–elevation data for terrace sites along the Rhine, thus enabling a more detailed reconstruction of the timing, rate, and spatial variability of uplift in the Rhenish Massif.

References
Lippolt, H.J., 1983. Distribution of volcanic activity in space and time. In: Fuchs, K., von Gehlen, K., Mälzer, H., Murawski, H., Semmel, A. (Eds.), Plateau Uplift. Springer, Berlin, pp. 112–120.
Meyer, W., Stets, J., 1998. Junge Tektonik im Rheinischen Schiefergebirge und ihre Quantifizierung. Z. dt. geol. Ges. 149, 359–379. https://doi.org/10.1127/zdgg/149/1998/359.