Palaeomagnetism of Cainozoic volcanics from Germany

地球流体外核中的自给自足发电机产生的地磁场对保护生物圈和通信卫星免受太阳风的侵袭至关重要。在地心轴偶极子的一级近似模型中，它也经历了被称为古分子变化(PSV)的方向和强度的自发波动，并且可以随机地反转它的极性，而不依赖于地幔施加在地核上的热边界条件的变化。反转频率、PSV幅度和偶极子场强的变化如何准确地联系在一起，仍然是一个有争议的问题。一方面，发电机数值模拟预测，磁场强度的变化与反转频率和PSV幅度的变化呈负相关，但它们是简化的物理模型，可能不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，我们调查了15-30 Ma埃塞俄比亚火山的古地磁，并记录了PSV与反转频率之间的局部关系，这与发电机模拟的预测不一致。为了阐明PSV和反转频率之间的这种可能的脱钩是局部的还是全球的特征，我们建议研究德国15-45 Ma火山岩的古地磁。德国最大的三个火山田--Vogelsberg(16-18 Ma)、Lausitz(29-32 Ma)和Hocheifel(35-37 Ma+39-44 Ma)--每个都由数百座以喷流为主的火山组成，这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PSV幅度、场强和局部尺度的反转频率之间的相关性之后，我们将汇编最可靠的现有PSV和API数据，以更好地描述地球磁场在15-45毫安间隔内在全球尺度上的几何形状和变化。这将包括检测PSV代理的偶极强度或纬度分布中可能存在的对比。我们还将使统计场模型与经验数据相适应，并注意分析方向性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.