Paleointensity of the time-averaged geomagnetic field at the Equator

在广泛的时间范围内描述地球磁场的特征对于理解核心发电机的产生机制是非常重要的。最近在南极埃里伯斯火山省78°S发表的结果表明，虚拟地磁极的高角散与明显异常的低古强度相结合，可能是与切线柱体有关的动力效应的结果。另一种解释是，时间平均场的地磁偶极矩实际上只有今天值的50%左右，这意味着从其他地方获得的古强度数据存在严重偏差。赤道带受切线柱体效应的影响最小，但可靠的古强度并不能很好地代表赤道带。我们建议从加拉帕戈斯群岛和肯尼亚的0-5 Myr古老熔岩流中产生古强度数据，这些数据最近提供了对低古分子变化的一致估计。古地磁、岩石磁学和古强度初步研究结果表明，这些岩石具有较好的磁性，可用于古强度实验。这些地点中的大多数都有新的亚样本，但我们想从肯尼亚的Loiyangalani地区收集更多的样本，那里有限的数据显示出非常连贯和稳定的磁化作用，几乎没有闪电。我们的总体目标是从用于估计古分子方向变化的相同熔岩中获得一个强大的古强度数据集，理想的情况是，产生赤道时间平均场的全矢量特征。这项拟议工作的成功完成将提供对地磁场行为的更准确描述，作为测量纬度变化的基准，包括与切线柱体有关的可能影响，以及早期古分子变化的基本特征。该项目将直接支持博士生的论文研究，并包括实验室、现场和普遍适用的分析技术方面的培训。

The characterization of Earth's magnetic field over a broad range of time scales is of fundamental importance for understanding the core dynamo generating mechanism. Recently published results from the Erebus Volcanic Province in Antarctica at 78°S suggested that the high angular dispersion in virtual geomagnetic poles coupled with apparently anomalously low paleointensities may result from dynamic effects associated with the tangent cylinder. An alternative explanation is that the geomagnetic dipole moment of the time-averaged field is in fact only about 50% of the present-day value, which would imply that available paleointensity data from elsewhere are seriously biased. The equatorial belt, which should be least affected by tangent cylinder effects, is poorly represented by reliable paleointensities. We propose to generate paleointensity data from 0-5 Myr-old lava flows from the Galapagos Islands and from Kenya, which have recently provided consistent estimates of low paleosecular variation. The paleomagnetic, rock magnetic and preliminary paleointensity results indicate that these rocks have suitable magnetic properties for Thellier-type paleointensity experiments. Fresh subspecimens are available from most of these sites but we would like to collect additional samples from the Loiyangalani area of Kenya, where the limited data show remarkably coherent and stable magnetizations virtually free of lightning strikes.Our overall objective is to obtain a robust paleointensity dataset from the same lavas used to estimate paleosecular variation in directions and ideally, to produce a full-vector characterization of the time-averaged field at the Equator. Successful completion of this proposed work will provide a more accurate description of geomagnetic field behavior as a benchmark to gauge latitudinal variations, including possible effects associated with the tangent cylinder, and the underlying character of paleosecular variation in earlier epochs. The project will directly support thesis research of a PhD student and include training in laboratory, field and analytical techniques of general applicability.