3-D structure of the lithosphere beneath the southern Rhine Graben area

Abstract

The 3-D velocity structure of the lithosphere-asthenosphere system beneath the southern Rhine Graben area is imaged by inverting P-wave traveltime residuals of teleseismic events recorded by a dense network of short-period stations. The upper part of the lithosphere, marked by velocity anomalies orientated along the graben strike can be related to the development of the graben. These upper 50 km display stronger lateral heterogeneities than the weak anomalies observed at deeper levels which show roughly an E-W orientation. The teleseismic inversion models yield no indications for significantly reduced seismic P-wave velocities in the upper mantle as could be expected from an actively upwelling mantle diapir located beneath the southern Rhine Graben area. The observation of generally weak P-wave velocity variations at greater depth indicates a rather smooth transition from the lower lithosphere to the upper asthenosphere. The observed heterogeneities in the 25–50 km depth range may be related to partial melts which intruded the mantle lithosphere during the middle and late Miocene. These melts cooled and solidified since that intrusion. The rifting and thermal doming stage of the Rhine Graben ceased at the end of the Miocene.