Palaeomagnetism of Cainozoic volcanics from Germany

德国新生代火山岩的古地磁学

• 批准号: 517539177
• 负责人: Privatdozent Dr. Florian Lhuillier
• 金额: --
• 依托单位: Department für Geo- und Umweltwissenschaften
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/517539177?language=en
• 关键词: Palaeomagnetism; Cainozoic; volcanics; Germany

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.

地磁场是由地球流体外核中的一个自我维持的发电机产生的，对于保护生物圈和电信卫星免受太阳风的影响至关重要。在第一近似模型的地心轴向偶极子，它也经历了自发波动的方向和强度称为palaeosecular变化（PSV），并可以stochastically扭转其极性的变化，在热边界条件所施加的地幔上的核心。反转频率、PSV振幅和偶极场强度的变化如何确切地联系在一起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。在以前的DFG项目中，我们研究了15-30 Ma埃塞俄比亚火山岩的古地磁，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一致。为了阐明PSV和反转频率之间的这种可能的解耦是否是局部或全球特征，我们建议调查德国15-45 Ma火山岩的古地磁。德国最大的三个火山区--Vogelsberg（16-18 Ma）、Lausitz（29-32 Ma）和Hocheifel（35-37 Ma + 39-44 Ma）--均由数百个主要喷发火山组成，为得出统计上可靠的PSV估计值和确定某些绝对古强度（API）提供了理想条件。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，我们将编制一份最可靠的PSV和API数据汇编，以更好地说明15-45 Ma间隔内全球尺度上地球磁场的几何形状和变化。这将包括检测偶极强度或PSV代理的纬度剖面中可能存在的对比。我们还将根据经验数据拟合统计场模型，并注意分析方向和强度数据集之间的相互兼容性。