Palaeomagnetism of Cainozoic volcanics from Germany

• Applicant: Privatdozent Dr. Florian Lhuillier
• Subject Area: Geophysics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 517539177

The geomagnetic field, generated by a self-sustaining dynamo in the Earth’s fluid outer core, is of first importance to shield the biosphere and the telecommunication satellites from the solar wind. Modelled in first approximation by a geocentric axial dipole, it also experiences spontaneous fluctuations in direction and intensity termed palaeosecular variation (PSV) and can stochastically reverse its polarity independent of changes in the thermal boundary condition imposed by the mantle on the core. How variations in reversal frequency, PSV amplitude and dipole field strength are exactly linked remains a controversial issue. On the one hand, numerical dynamo simulations predict that variations in field strength negatively correlate with the variations in reversal frequency and PSV amplitude, yet they are simplified physical models that may not be directly applicable to the Earth’s magnetic field. On the other hand, palaeomagnetic records directly witness the evolution of the Earth’s magnetic field, yet they need to meet strict requirements to provide statistically robust inferences. In a previous DFG project, we investigated the palaeomagnetism of 15–30 Ma Ethiopian volcanics and documented a local relationship between PSV and reversal frequency that was incompatible with the predictions from dynamo simulations. To elucidate whether this possible decoupling between PSV and reversal frequency is a local or global feature, we propose to investigate the palaeomagnetism of 15–45 Ma volcanics in Germany. Three of the largest German volcanic fields—Vogelsberg (16–18 Ma), Lausitz (29–32 Ma) and Hocheifel (35–37 Ma + 39–44 Ma)—each consist of several hundreds of dominantly effusive volcanoes, offering ideal conditions to derive statistically robust PSV estimates and determine some absolute palaeointensities (API). After analysing the correlations between PSV amplitude, field strength and reversal frequency at a local scale, we will produce a compilation of the most robust available PSV and API data to better characterise the geometry and variability of the Earth’s magnetic field at a global scale over the 15–45 Ma interval. This will include the detection of possible contrasts in the dipole strength or in the latitudinal profile of the PSV proxies. We will also fit statistical field models to the empirical data, taking care of analysing the mutual compatibility between directional and intensity datasets.

• DFG Programme: Research Grants