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Shah, Jay; Koppers, Anthony A. P.; Leitner, Marko; Leonhardt, Roman; Muxworthy, Adrian R.; Heunemann, Christoph; Bachtadse, Valerian ORCID: 0000-0002-1226-2986; Ashley, Jack A. D.; Matzka, Jürgen (2016): Palaeomagnetic evidence for the persistence or geomagnetic main field anomalies in the South Atlantic. In: Earth and Planetary Science Letters, Vol. 441: pp. 113-124
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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 mu T, compared to an expected value of similar to 43 mu T;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 Ar-40/Ar-39 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 mu T and virtual axial dipole moment (VADM) of 3.1 +/- 1.2 x 10(22) Am-2. 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. (C) 2016 Elsevier B.V. All rights reserved.