Palaeomagnetism of Cainozoic volcanics from Germany

地磁场是由地球流体外核中的自持发电机产生的，它对保护生物圈和电信卫星免受太阳风的影响至关重要。它也经历了方向和强度的自发波动，称为古长期变化（PSV），并且可以随机地逆转其极性，而不依赖于地幔对地核施加的热边界条件的变化。反转频率、PSV振幅和偶极子场强的变化是如何准确联系起来的，仍然是一个有争议的问题。一方面，数值发电机模拟预测磁场强度的变化与反转频率和PSV振幅的变化呈负相关，但它们是简化的物理模型，可能不能直接适用于地球磁场。另一方面，古地磁记录直接见证了地球磁场的演变，但它们需要满足严格的要求，才能提供统计上可靠的推断。在之前的DFG项目中，我们研究了15-30 Ma埃塞俄比亚火山的古地磁，并记录了PSV和反转频率之间的局部关系，这与发电机模拟的预测不相容。为了阐明PSV与反转频率之间可能的解耦是局部的还是全球的特征，我们建议对德国15-45 Ma火山的古地磁进行研究。德国最大的三个火山场——vogelsberg (16-18 Ma), Lausitz （29-32 Ma）和Hocheifel （35-37 Ma + 39-44 Ma）——每个火山场都由数百个主要的喷发火山组成，为得出统计上可靠的PSV估计和确定一些绝对古强度（API）提供了理想的条件。在分析了局部尺度上PSV振幅、场强和反转频率之间的相关性之后，我们将生成最可靠的PSV和API数据汇编，以更好地表征全球尺度上15-45 Ma区间内地球磁场的几何形状和可变性。这将包括检测偶极子强度或PSV代理的纬向剖面的可能对比。我们还将统计场模型拟合到经验数据中，注意分析方向和强度数据集之间的相互兼容性。

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.