Integrated geophysical-petrological modelling of the Eifel region

We present an integrated geophysical-petrological model of the Eifel region. The Eifel is a volcanic active region in West Germany that exhibits Tertiary as well as Quaternary volcanism. One suggestion for the source of this volcanism is a small-scale upper mantle plume.

The 3D model includes the crust and upper mantle and was generated by combined modelling of topography and the gravity field with constraints from seismology and geochemistry. In the best-fit model, the subcontinental lithospheric mantle is associated with a Phanerozoic-type composition, resulting in a depth of 80 km for the lithosphere-asthenosphere boundary (LAB) beneath the Eifel and in comparison 110 - 130 km beneath the Paris basin. A Proterozoic-type composition in contrast results in a LAB depth of 120 km in the Eifel. While the model fits the geophysical observables and features a thin lithosphere, it does not lead to a plume-like structure and does not feature a seismic low-velocity anomaly.

The measured low-velocity anomaly can be reproduced by introducing (1) an even thinner lithosphere or (2) a plume-like body above the thermal LAB with a composition based on data from Eifel xenoliths, which have a mainly basanitic composition. This additional structure results in a thermal anomaly and has an effect on the isostatic elevation of c. 360 m, but it does not result in a significant signal in the gravity anomalies. Further modelling showed how crustal intrusions could additionally mask the gravitational effect from such a small-scale upper mantle plume.

The model does not conclusively explain the source of the Eifel volcanism, but the models and the calculation of synthetic dispersion curves help to assess the possibility to resolve a small-scale upper mantle plume with joint inversion in future analysis.