Palaeomagnetic variations across transitional lava flows: geomagnetic-field impulses or recording artifacts?

在斯蒂恩斯山观测到的快速磁场变化被有争议地解释为：它们要么是岩石磁性不均匀造成的人工产物，要么反映了地磁场的变化。如果变化来自内部，后一种可能性将对地球发电机理论产生重要影响，如果变化是由于外部磁场活动增强，则对过渡电离层和磁层具有重要影响。关于斯蒂恩斯山脉层序的几项研究未能解决这个问题。因此，为了找到支持或反对高动态过渡场的证据，我们建议调查来自其他有良好记录的方向和强度记录的过渡性熔岩流动。在我们的准备工作中，我们开发了一种采样策略和测量技术，以发现冷却熔岩流中记录的快速变化。这一新方法将使我们能够评估变化是否源于地磁，并确定表明外部来源的周期性场变化。在拟议的项目中，我们计划将这种方法应用于冰岛R3-N3反转产生的气流，在那里观察到强烈的赤道偶极子，并将这种方法应用于从大加那利岛埃尔帕索反转产生的C-TP62流的已经采样的剖面，该剖面产生了极低的古强度值(1.2微吨)。我们的测量将提供这些流的高分辨率岩石和古地磁剖面，这将有助于制定最佳古地磁测量策略，并测试用于对其NRM可能受到后来再加热影响的熔岩流进行古地磁采样的可靠性标准。我们也有独特的机会发现由于外部场源或异常高的地磁场变化率而导致的每日变化，然后可以通过我们固有的一致性检查来验证这一点。

Rapid field variations observed at Steens Mountain are interpreted controversially: Either they are artifacts due to rock magnetic inhomogeneity or they reflect geomagnetic field changes. The latter possibility would have important implications for geodynamo theory if the variation is of internal origin, or for the transitional ionosphere and magnetosphere if the change is due to enhanced external field activity. Several studies on the Steens Mountain sequence failed to resolve this question. Therefore, to find evidence for or against highly dynamic transitional fields, we propose to investigate transitional lava flows from other locations with well documented directional and intensity records. In our preparatory work, we have developed a sampling strategy and measurement technique to discover rapid variations recorded in cooling lava flows. This new approach will allow us to assess if variations are of geomagnetic origin and to identify periodic field variations indicative of external sources. In the proposed project, we plan to apply this method to flows from the R3-N3 reversal on Iceland, where strong equatorial dipoles were observed, and to an already sampled profile across flow C-TP62 from the El Paso reversal on Gran Canaria, which yielded extremely low palaeointensity values (1.2 µT). Our measurements will provide high resolution rock- and palaeomagnetic profiles across these flows which will serve to develop optimum palaeointensity measurement strategies and to test reliability criteria used for palaeomagnetic sampling of lava flows whose NRM might have been affected by later reheating. We also have the unique chance to discover daily variations due to external field sources or unusually high rates of geomagnetic field variation, which then can be verified by our intrinsic consistency check.