Large-scale mantle heterogeneity beneath the Rhenish Massif and its vicinity from teleseismic P-residuals measurements.

Abstract

The azimuthal variation of teleseismic P-residuals observed at 63 stations in the vicinity of the Rhenish massif for 350 events world-wide provides unequivocal evidence for large-scale mantle heterogeneity beneath this area. All the models for the velocity anomalies causing this variation are extremely similar and produce a variance improvement of at least 74%. Their main features include low velocity structures associated with the regions of volcanism and high velocities beneath the southern Rhine graben-Vosges-Black Forest area. The major anomaly lies beneath the West Eifel, where there is a velocity decrease of 3-5% extending from approx 50-200 km depth. This structure is consistent with models for the uplift mechanism which involve lithospheric thinning or expansion of the mantle due to metasomatism and partial melting. The partial melt hypothesis is favoured on the basis of gravity and seismic refraction data.-J.M.H.