Collaborative Research: Paleomagnetic Investigation of Quaternary Volcanics from Kenya and the Galapagos Islands: In Search of the Time-Averaged Magnetic Equator

本研究旨在从肯尼亚更新世（0-1.7 Ma）正极性和反极性熔岩流中获得高质量的古地磁数据，以约束赤道的时间平均磁场并确定时间平均磁赤道。先前对厄瓜多尔赤道熔岩的研究（Opdyke et al.， g -立方，修订版）得出的假设是，赤道磁场的最佳模型是对地心轴向偶极子场贡献约5%的轴向四极子。该模型预测,地磁场的纬度大约3 deg.北将水平和代表的位置上磁赤道而在地理赤道倾斜大约4度。这些差异很小但可检测大型数据集,我们希望获得从赤道附近的熔岩太肯尼亚和赤道以北大约3 deg. Loyangalani周围地区在东部海岸的图尔卡纳湖,东部有一座巨大的火山库拉尔火山，图尔卡纳湖南岸的格雷戈里裂谷也有大量的熔岩流，可以采集样本。采样将在两年内进行两次采样旅行，每次持续时间约为一个月。时间平均地磁场预计在地球自转轴周围是对称的，这项研究将验证这一假设，因为拟议研究的区域位于厄瓜多尔以东135度。还将从从加拉帕戈斯群岛收集的80个地点的样本中获取和处理数据。Rochette et al.（1997）报告了样品收集的初步结果，钻孔岩心的未使用部分将被完全消磁。早期的古强度研究将在肯尼亚和加拉帕戈斯收集的精选样本上进行，以试图获得古场的完整矢量特征。因此，在本研究结束时，将从赤道附近（厄瓜多尔、肯尼亚和加拉帕戈斯群岛）的三个大型熔岩研究中获得高质量的古地磁数据，这些数据将大大增加对时间平均地磁场结构的认识。这项工作的更广泛影响之一是培养毕业生和本科生。

The study seeks to obtain high-quality paleomagnetic data from normal and reverse polarity lava flows of Pleistocene age (0-1.7 Ma) from Kenya to constrain the time-averaged field at the equator and to determine the Time-Averaged Magnetic Equator. A previous study on equatorial lavas from Ecuador (Opdyke et al., G-cubed, in revision) leads to the hypothesis that the magnetic field at the equator is best modeled with a ~5% axial quadrupole contribution to the geocentric axial dipole field. This model predicts that the geomagnetic field at a latitude of approximately 3 deg. north will be horizontal and represent the position of the Time-Averaged Magnetic Equator whereas at the geographical equator it will be inclined about 4 deg. These differences are small but detectable with the large data sets that we hope to obtain from lavas at the equator in the vicinity of Mt Kenya and about 3 deg. north of the equator in the area around Loyangalani on the east shore of Lake Turkana, where a large volcano, Mt. Kulal, lies just to the east and there are also voluminous lava flows in the Gregory rift on the southern shore of Lake Turkana that can be sampled. Sampling will be done over two years in two sampling trips each of about a month's duration. The time-averaged geomagnetic field is expected to be symmetrical around the Earth's spin axis and this study will test that hypothesis since the region of the proposed study is 135 deg. east from Ecuador. Data will also obtained and processed from samples from 80 sites collected from the Galapagos Islands. Preliminary results for this sample collection were reported by Rochette et al. (1997) and the unused portions of the drill cores will be fully demagnetized. Thellier paleointensity studies will be done on selected samples from both the Kenya and the Galapagos collections in an attempt to obtain a full vector characterization of the paleofield. Therefore, at the conclusion of this study, high-quality paleomagnetic data will be available from three large studies of lavas from near the equator (Equador, Kenya and Galapagos Islands) and these data will greatly increase the knowledge of the configuration of the time-averaged geomagnetic field. Among the broader impacts of this work are training of graduates and undergraduates.