Palaeomagnetic evidence for the persistence or recurrence of geomagnetic main field anomalies in the South Atlantic
File(s)
Author(s)
Type
Journal Article
Abstract
We present a dataset of a full-vector palaeomagnetic study of Late Pleistocene lavas from the island Tristan da Cunha in the South Atlantic Ocean. The current day geomagnetic field intensity in this region is approximately 25 μT, compared to an expected value of ∼43 μT; this phenomenon is known as the South Atlantic geomagnetic Anomaly (SAA). Geomagnetic field models extending back to the last 10 ka find no evidence for this being a persistent feature of the geomagnetic field, albeit, all models are constructed from data which is particularly sparse in the southern hemisphere. New 40Ar/39Ar incremental heating dating indicates the studied lavas from Tristan da Cunha extruded between 90 and 46 ka. Palaeointensity estimations of eight lava flows made using the Thellier method yield an average palaeointensity of 18±6 μT and virtual axial dipole moment (VADM) of 3.1±1.2×1022 Am2. The lava flows demonstrate four time intervals comparable to the present day SAA, where the average VADM of the Tristan da Cunha lavas is weaker than the global VADM average. This suggests a persistent or recurring low intensity anomaly to the main geomagnetic field similar to the SAA existed in the South Atlantic between 46 and 90 ka.
Date Issued
2016-03-09
Date Acceptance
2016-02-17
Citation
Earth and Planetary Science Letters, 2016, 441, pp.113-124
ISSN
1385-013X
Publisher
Elsevier
Start Page
113
End Page
124
Journal / Book Title
Earth and Planetary Science Letters
Volume
441
Copyright Statement
© 2016, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/
Subjects
Geochemistry & Geophysics
02 Physical Sciences
04 Earth Sciences
Publication Status
Published