Integrated geophysical-petrological modelling of the Eifel region

<p>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.</p><p>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.</p><p>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.</p><p>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.</p>

Six days in July: Charles Lyell in the Eifel in 1831 (possibly looking at loess)

Charles Lyell made a geological excursion to the Eifel region in Germany in July 1831. He went to examine volcanic rocks and volcanic landscapes. He discussed this outing with Mary Somerville and Samuel & Charlotte Hibbert. It is possible that he observed loess in the Eifel. It is hoped that his Eifel notebook is with the Lyell papers at Kinnordy and that it may be transcribed and published. Lyell spread the word on loess; Von Leonard invented it and Horner enthused about it but Lyell disseminated the essential idea of loess. There is (so far) no clear evidence that Lyell saw and appreciated loess in the Eifel region in 1831. This suggests that his first real encounter with the loess (ground or concept) was in the discussions with the Hibberts in September 1831. He certainly had substantial (reported) encounters in 1832, and was definitely interested by the time of the publication of the Principles of Geology vol. 3 in 1833.

New Minerals from the Classic Eifel Region

In the recent four years, the authors have jointly organized and conducted several excursions into the classical volcanic field in the Eifel area, Germany. The original goal was to compare its geochemistry and mineralogy with those of the hyperalkaline intrusions of Khibiny and Lovozero on Kola peninsula, Russia. Since none of us had previous experience with the Eifel area, local amateur mineral collectors were contacted and asked for support. These collectors often have been active in their region for decades and, hence, know the various deposits and minerals by heart. Our request was met with great enthusiasm and invaluable support was given to us not only with respect to the organization of the excursions, but the collectors also shared their experience with getting access to the quarries and often offered samples from their own, very well organized and documented, collections. It soon turned out, that – a bit to our surprise - even in such a classical area as the Eifel with its long tradition of geological and mineralogical research new minerals can be found. As a result, 16 new minerals from the Eifel could be described, accepted by IMA, and the results published. Others are still under study. Some of these minerals were found in the field, others were donated by local mineral collectors. In acknowledgement of their invaluable contribution, several minerals now bear names of those or other local collectors. Several of the new minerals belong to well-known mineral groups, but a few represent quite new structures. For example, in the mineral hielscherite, the pyramidal sulfite anion substitutes for planar carbonate in thaumasite, and günterblassite is the first phyllosilicate with a triple tetrahedral layer, thus indicating somehow a structural transition into a tectosilicate.