Changes in Non‐Dipolar Field Structure Over the Plio‐Pleistocene: New Paleointensity Results From Hawai'i Compared to Global Data Sets
Changes in Non‐Dipolar Field Structure Over the Plio‐Pleistocene: New Paleointensity Results From Hawai'i Compared to Global Data Sets
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DOI：
10.1029/2023jb026492
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发表时间：
2023-05
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影响因子：
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通讯作者：
B. Cych;L. Tauxe;G. Cromwell;J. Sinton;A. Koppers
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作者：
B. Cych;L. Tauxe;G. Cromwell;J. Sinton;A. Koppers
古地磁学的一个基本假设是，当在足够的时间尺度上进行平均时，地球磁场表现为地心轴偶极子（GAD）。对过去 5 Ma 平均方向数据的编译产生了与 GAD 很大程度上兼容的分布，但该时间尺度上的古强度数据的分布是不兼容的。 GAD失败的原因包括： (a) 消除“不可靠”数据的任意“选择标准”因研究而异，因此古强度数据库可能包含有偏差的结果。 (b) 现有古强度数据的年龄分布随纬度的不同而变化，因此不同的纬度平均值代表不同的时间段。 (c) 时间平均场可能是真正的非偶极场。在这里，我们提出了一种一致的方法来分析古强度结果并比较不同研究的时间平均古强度。我们将其应用于来自普里奥/更新世夏威夷火成岩的数据，这些数据是从细粒、快速冷却的材料（熔岩流顶部、岩脉边缘和火山渣锥）中采样的，并采用了 IZZI-Thellier 技术；使用 Cych 等人的古强度偏差校正估计方法对数据进行分析。 （2021，https://doi.org/10.1029/2021GC009755），它可以产生准确的古强度估计，而不会任意从分析中排除样本。我们使用 Livermore 等人的方法构建了夏威夷在上皮里奥/更新世的古强度曲线。 （2018，https://doi.org/10.1093/gji/ggy383），它解释了数据的年龄分布。我们证明，即使从时间稀疏数据中获得平均场存在很大的不确定性，我们从夏威夷和南极洲获得的平均古强度（从 Asefaw 等人，2021 年重新分析，https://doi.org/10.1029/2020JB020834）在 0 到 1.5 Ma 期间并不像 GAD，但可能早于该时间。
A foundational assumption in paleomagnetism is that the Earth's magnetic field behaves as a geocentric axial dipole (GAD) when averaged over sufficient timescales. Compilations of directional data averaged over the past 5 Ma yield a distribution largely compatible with GAD, but the distribution of paleointensity data over this timescale is incompatible. Reasons for the failure of GAD include: (a) Arbitrary “selection criteria” to eliminate “unreliable” data vary among studies, so the paleointensity database may include biased results. (b) The age distribution of existing paleointensity data varies with latitude, so different latitudinal averages represent different time periods. (c) The time‐averaged field could be truly non‐dipolar. Here, we present a consistent methodology for analyzing paleointensity results and comparing time‐averaged paleointensities from different studies. We apply it to data from Plio/Pleistocene Hawai'ian igneous rocks, sampled from fine‐grained, quickly cooled material (lava flow tops, dike margins and scoria cones) and subjected to the IZZI‐Thellier technique; the data were analyzed using the Bias Corrected Estimation of Paleointensity method of Cych et al. (2021, https://doi.org/10.1029/2021GC009755), which produces accurate paleointensity estimates without arbitrarily excluding specimens from the analysis. We constructed a paleointensity curve for Hawai'i over the Plio/Pleistocene using the method of Livermore et al. (2018, https://doi.org/10.1093/gji/ggy383), which accounts for the age distribution of data. We demonstrate that even with the large uncertainties associated with obtaining a mean field from temporally sparse data, our average paleointensities obtained from Hawai'i and Antarctica (reanalyzed from Asefaw et al., 2021, https://doi.org/10.1029/2020JB020834) are not GAD‐like from 0 to 1.5 Ma but may be prior to that.