Absolute paleointensities on cretaceous kimberlites in Botswana

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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.