Absolute paleointensities on cretaceous kimberlites in Botswana

超级计时器提供了一个绝佳的机会来检验关于地球液态外核对流和地磁场产生的各种理论和模型。为了获得完整的地球动力学图像，除了过去主要确定的古方向外，确定古强度也是至关重要的。到目前为止，只有少数研究收集了过去160毫安的强度数据。研究结果的多样性导致了三种不同的古强度长期变化模式（1 .中生代平均古强度低于新生代；2 .近0.3 Ma古强度明显高于此前；3 .白垩纪正超时（CNS）古强度较高）。尤其需要更多高质量的数据，以使CNS能够确认或拒绝这些模型，并在不同的地球动力学理论之间做出决定。白垩纪时代的金伯利岩在非洲南部相当多，可能为CNS提供获得大量强度数据的机会。因此，本研究的目标是对博茨瓦纳的各种金伯利岩管道进行取样，并检查它们对古强度测定的适用性。以前的研究主要集中在它们的古方向特征上，得到了非常可靠的数据，由此得出的古磁极构成了非洲表观极移路径的重要组成部分。然而，无论是原位还是实验过程中的变化，都会使古强度的测定复杂化，并且由于冷却速率、剩余物的磁各向异性和磁畴态偏置的差异，可能会产生进一步的问题。因此，计划结合古强度测定进行详细的岩石磁学和古定向研究，以获得有关金伯利岩剩余物获取过程的完整知识。如果古强度测定成为可能，我们将能够显著增加古强度数据集。

Superchrons provide a remarkable opportunity to test the various theories and models regarding convection in the Earth’s liquid outer core and the generation of the geomagnetic field. To obtain a complete picture of the geodynamo, determination of the paleointensity is crucial in addition to paleodirections, which were mainly determined in the past. So far only few studies have collected intensity data for the last 160 Ma. The great variety of their results led to three different models of long-term paleointensity changes (1: lower mean paleointensity during the Mesozoic than during the Cenozoic; 2: significantly higher intensity in the last 0.3 Ma than prior to that; 3: high mean paleointensity during the Cretaceous Normal Superchron, CNS). Much more high quality data is needed especially for the CNS to be able to confirm or reject these models and to decide between the different theories of the geodynamo. Kimberlites of cretaceous age, which are quite numerous in southern Africa, may provide an opportunity to obtain a high amount of intensity data for the CNS. The target of this study is, thus, to sample a variety of kimberlite pipes in Botswana and to check their suitability for paleointensity determination. Previous studies, which have focused on their paleodirectional characteristics, yielded very reliable data and the resulting paleomagnetic poles form an important part of Africa’s apparent polar wander path. However, alterations, either in situ or during the experiment, complicate paleointensity determination and further problems may arise due to differences in cooling rates, magnetic anisotropy of the remanence and magnetic domain state bias. It is therefore planned to carry out detailed rock magnetic and paleodirectional studies in combination with paleo-intensity determinations in order to gain complete knowledge about remanence acquisition processes in kimberlites. If paleointensity determinations turn out to be possible, we will be able to significantly increase the paleointensity data set.