Absolute paleointensities on cretaceous kimberlites in Botswana

超级计时器提供了一个极好的机会来测试关于地球液态外核对流和地磁场产生的各种理论和模型。为了获得地球发电机的完整图像，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，只有很少的研究收集了最近160 Ma的强度数据。结果的巨大差异导致了三种不同的长期古强度变化模式(1：中生代的平均古强度低于新生代；2：最后0.3 Ma的强度明显高于之前；3：白垩纪正常超时时期的高平均古强度)。需要更多高质量的数据，特别是为了让CNS能够确认或拒绝这些模型，并在不同的地球发电机理论之间做出决定。南部非洲白垩纪的金伯利岩数量相当多，可能为获得中南半球的高强度数据提供了机会。因此，这项研究的目标是对博茨瓦纳的各种金伯利岩管进行采样，并检查它们是否适合于古强度测定。以前的研究侧重于它们的古方向特征，产生了非常可靠的数据，由此产生的古地磁极构成了非洲明显的极地漂移路径的重要组成部分。然而，无论是在现场还是在实验过程中的变化，都使古强度测定变得复杂，而且由于冷却速度、剩磁的磁各向异性和磁畴态偏置的差异，可能会出现进一步的问题。因此，计划结合古强度测定开展详细的岩石、磁性和古方向研究，以全面了解金伯利岩中剩磁的获取过程。如果古强度测定最终成为可能，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.