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. Here, we present the first isochron-burial ages for the OMT and YMT at two sites. At Kasbach-Ohlenberg, we obtain an age of 1.56 ( +0.15 / −0.14 ) for the OMT and 0.76 ( +0.19 / −0.17 ) Ma for the YMT, respectively. These ages and the small vertical distance of 4 m between both terraces indicate a long period with negligible river incision, followed by a phase of rapid incision and rock uplift. The height of the YMT above the Rhine (i.e., 157 m) yields an average uplift rate of ~200 m/Ma during this phase. Near Bad Hönningen, the age of the OMT is 1.25 ( +0.16 / −0.15 ) Ma. The younger age and higher elevation of the OMT at this site suggest that rock uplift increases toward the internal part of the Rhenish Massif. The coincidence between the onset of uplift and the beginning of plume-related intraplate volcanism at ~700 ka indicates that the uplift of the Rhenish Massif is driven by a buoyant mantle plume.