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Abstract 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.
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This content will become publicly available on April 1, 2026
Analysis of Paleointensity Results Under Different Interpretation Approaches: A Case Study on the Korkhi Volcanic Sequence (Lesser Caucasus, Georgia)
Abstract In this study we focus on the investigation of the absolute intensity records of two volcanic subsequences, aiming to enrich the global paleointensity database for the last 5 Ma, which currently shows important dispersion. We present new absolute paleointensities obtained from the Plio‐Pleistocene volcanic sequence of Korkhi (Djavakheti Highland, Georgia) (41°27′31″N, 43°27′55″E). Korkhi is divided into two lava flow subsequences dated at 3.11 ± 0.20 Ma and 1.85 ± 0.08 Ma. Paleomagnetic directions previously published (Sánchez‐Moreno et al., 2018,https://doi.org/10.1029/2017GC007358) show a normal polarity in the lower Korkhi subsequence and a reverse‐to‐intermediate polarity in the upper Korkhi subsequence. The new paleointensity determinations are obtained through two different Thellier‐type protocols (Thellier‐Thellier and IZZI) and the corrected multispecimen method. We utilize different selection criteria and interpretation approaches (TTB, CCRIT, BiCEP and multimethod), and we make a critical evaluation on their application on complex magnetic behaviors, such as often found in volcanic rocks. Finally, we obtained a paleointensity of 70 μT in upper Korkhi and 14 paleointensities in lower Korkhi that vary between 5.2 and 37.2 μT. These results agree with a recently proposed non‐Geocentric Axial Dipole (GAD) hypothesis for the last ∼1.5 Ma (Cych et al., 2023,https://doi.org/10.1029/2023JB026492), and with low field strength for the 3–4 Ma.
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- Award ID(s):
- 2245628
- PAR ID:
- 10588750
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 26
- Issue:
- 4
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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