Miocene time-averaged geomagnetic field model suggests long lived mantle control and recurring structure in the South Atlantic

Engbers, YA, Holme, R and Biggin, AJ ORCID: 0000-0003-4164-5924
(2024) Miocene time-averaged geomagnetic field model suggests long lived mantle control and recurring structure in the South Atlantic. Earth and Planetary Science Letters, 626. p. 118535.

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Reconstructions of long-term time-averaged geomagnetic field structures are important to understand geomagnetic field evolution and to identify the longevity and scale of non-dipolar field morphology. This study presents MTAM1, a non-zonal time-averaged field model for the Miocene era (5.3–23 million years ago), or indeed any time period prior to 5 million years ago. The time averaged field model for the Miocene is an inverse model based on a directional data compilation comprising 38 different localities, each with a minimum of 10 sites, called PSVM (Engbers et al., 2022a). The data were separated into normal (PSVMN) and normalised reversed (PSVMR) datasets, yielding two corresponding models MTAM1N and MTAM1R. Allowing for the opposite sign, no substantial differences were found between these two models, suggesting symmetry between the morphology of the normal and reversed fields and no evidence for non-reversing features in the geomagnetic field. Under this assumption of symmetry, the normal and reversed data can be modelled together, enhancing the data distribution and thus the robustness of the complete time-averaged field model for the Miocene. The broad structure of the models resembles previous time-averaged field models for the past 5 Myr but there are some clear differences, particularly under the South Atlantic, where all Miocene models include a reversed flux patch (RFP). To investigate whether this difference is well defined, or could result from differences in modelling methodology or data distribution, the data of the last 5 Myr were inverted with our normal model for the Miocene as a prior constraint. We find no evidence that the Miocene model is inconsistent with the field structures required by data from the past 5 Myr, suggesting an overall stability in the averaged geomagnetic field morphology for the past 23 Myr. This is consistent with long-term mantle control on geomagnetic field morphology leading to consistent deviations from the geocentric axial dipole on a multi-million-year timescale on the Core-Mantle boundary (CMB).

Item Type: Article
Divisions: Faculty of Science and Engineering > School of Environmental Sciences
Depositing User: Symplectic Admin
Date Deposited: 11 Jan 2024 08:39
Last Modified: 11 Jan 2024 09:54
DOI: 10.1016/j.epsl.2023.118535
Open Access URL: https://www.sciencedirect.com/science/article/pii/...
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3177799