Geophysical site characterization in the vicinity of the Laacher See to image deep reaching fluid pathways in the Eifel (Germany) using Magnetotellurics (LaSEMI)

• Applicant: Privatdozentin Dr. Ute Weckmann
• Subject Area: Geophysics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560481964

The Eifel region is a part of the Hercynian Rhenish Massif forming a peneplain mainly composed of Palaeozoic metamorphic rocks. Intraplate volcanic activity occurred in the Eifel Volcanic Field (EVF) and a period of Quaternary volcanism continued until 11, 000 yr, including the explosive eruption of Laacher See (LSV) in the eastern EVF 12, 900 yr. The observed volcanic activity beneath Laacher See manifests in several gas seeps in the lake and its surrounding shore, emitting CO2 of magmatic origin. The existence of low seismic velocity zones in the mantle and crust as well as a mantle plume have been hypothesized for the EVF. Recently, a maximum uplift of 1mm/yr estimated from a GPS network as well as deep low-frequency earthquakes were reported - both hinting at magmatic activity. Compilation of different geophysical and -chemical data suggest a Moho upwelling, and an anomalous low-velocity gradient layer that could be connected by a vertical pathway towards the LSV. Such 3D features can be mapped by the electrical conductivity, as this parameter is very sensitive to fluids, magma and volatile compounds. Motivated by this, the magnetotelluric method (MT) was successfully applied to an other Variscan massif, the Bohemian Massif showing conductive fluid pathways beneath the mineral spas and the mofette fields. In response to the announcement of the ICDP workshop towards an Eifel drilling and to complement the ongoing seismic Large-N Eifel Experiment, I propose a broad-band MT array experiment centred at the LSV using broad-band full MT stations accompanied by telluric stations. With this geophysical site characterization, my aim is to image the electrical conductivity distribution in the East EVF throughout the crust and parts of the lithosphere for the first time, focusing on the structure below the LSV. Advanced data processing approaches will be necessary and viral to obtain a high quality and invertable MT data set. Using 2D and 3D inversion, we will obtain a first detailed 3D image of magma ascent pathways, crustal fluids and the shallow hydrothermal system. This proposed approach will be complemented with already acquired high-frequency Radio-Magnetotelluric data and legacy long period data, allowing to include the results into a regional context. In essence, the first 3D conductivity model of this area will be used to (i) create conceptual models incorporating existing results from other geoscience research; (ii) provide input for other disciplines, like geochemistry and hydrology, which are active in the EVF region, by quantification the amount and nature of fluids; and (iii) make recommendations on optimal locations and concepts for future drilling.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1006: Infrastructure area - International Continental Scientific Drilling Program (ICDP)
• Co-Investigator: Privatdozent Dr. Alexander Grayver