The Rhenish shield in Central Europe is made up by a series of slates, quartzites and limestones of dominantly Devonian age which were strongly folded by the Hercynian orogeny. The area has been uplifted to about 300 m since the Pliocene. Rates of uplift increased during the last 600,000 years as shown in the uplifted terraces of the Rhine river. The drainage pattern was forced to erode deep antecedent river valleys in the uplifted plateau. Two late Quaternary volcanic fields have developed on the Rhenish shield: The West Eifel, covering an area of some 500-600 km2 with c. 220 eruptive centers; and, about 25 km to the east, the smaller East Eifel (Laacher See area) with some 70 volcanic centers distributed over c. 400 km2. Magmas of both fields are moderately potassic. Most West Eifel magmas are nephelinites and leucitites and have high CaO/Al2O3-ratios (up to about 1.45) and 87 86Sr-ratios (0.7039-0.7044); in contrast, intermediate (tephritic) and highly differentiated (phonolitic) magmas are common in the East Eifel, where magma chambers of different compositions have developed at varying depths in the crust, as evidenced by a variety of crustal xenoliths. Primitive East Eifel magmas are dominantly basanites with Mg numbers <67, and very high 87 86Sr-ratios (0.7041-0.7047). The Quaternary Eifel magmas must have come from a different mantle area than the Tertiary magmas, whose 87 86Sr-ratio ranges from 0.7035-0.7040. Most of the existing seismic-refraction profiles in the Rhenish shield have been reinterpreted using travel time and amplitude information. The general pattern of observed phases can be divided into three types:. (1)Throughout the central shield a strong P-phase reflection from the crust-mantle boundary is recorded. The average crustal thickness is 28-29 km and the average crustal velocity is 6.2-6.3 km/sec. (2)Beneath the southern part of the shield strongly reflected phases show clear intracrustal and Moho discontinuities. Along profiles crossing major volcanic features the Mdiscontinuity is disrupted and an intermediate intracrustal boundary at about 20 km depth forms the main reflector. Beneath this boundary the velocity increases gradually from about 7 km/sec to upper-mantle velocities. (3)For profiles crossing the northern Rhinegraben area as well as for a line east of the Lower Rhine embayment, the observed phases indicate only one major seismic boundary at a depth of about 23 km where the velocity increases to 7.3 km/sec. Below this boundary the velocity increases gradually with depth reaching 8 km/sec at 27-28 km. The Rhenish shield is part of an incoherent block mosaic of the Alpine foreland. The Alps are under rapid Holocene uplift and sideward extension. Between the Alps and the Rhenish shield there is a major foreland block which is shifted northwestward to be sheared along the Rhinegraben rift with a sinistral polarity. The northern apex of this block wedges in the Rhenish shield and provokes an axial deformation and, conditioned by that, a split-up of the northwestward frame of the shield. It is shown that the shield uplift evolved as a consequence of horizontal deformations of the unit. Subcrustal rift propagation under the tectonically incompetent crustal unit of the Rhenish shield had favored magmatic activity, thermal rise and subsequent plateau uplift. © 1979.
