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Single Phase Oxidation of Ferrimagnetic Grains as a Cause of L-Shaped Arai–Nagata Diagrams

Authors
  • Shcherbakov, V. P.1
  • Gribov, S. K.1
  • Aphinogenova, N. A.1
  • Tselmovich, V. A.1
  • 1 Geophysical Observatory “Borok,” Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Borok, Yaroslavl oblast, 152742, Russia , Borok (Russia)
Type
Published Article
Journal
Izvestiya, Physics of the Solid Earth
Publisher
Pleiades Publishing
Publication Date
Sep 01, 2020
Volume
56
Issue
5
Pages
665–674
Identifiers
DOI: 10.1134/S1069351320050109
Source
Springer Nature
Keywords
License
Yellow

Abstract

Abstract—The experiments on the determination of paleointensity Banc of the Earth’s magnetic field by Thellier method on basalts of the Berd (Jurassic) and Paravakar (Cretaceous) collections sampled in the northeastern Armenia in 2006 revealed an anomalous behavior of the Arai–Nagata diagrams. The anomaly manifests itself by a sharp drop in the intensity of natural remanent magnetization (NRM) under heating of samples to about 400°C, which is accompanied by a very weak acquisition of partial thermoremanent magnetizations (pTRMs) in this temperature interval. The further increase in temperature leads to the opposite phenomenon—an unexpectedly sharp rise in pTRMs intensity with almost no decrease in NRM, which creates the L-shape of the Arai–Nagata diagram. A similar phenomenon of a steep decline during thermal demagnetization was also established for remanent saturation magnetization Mrs(T). We carried out a number of magnetomineralogical experiments from which we conclude that, consistent with the hypothesis suggested by (Kosterov and Prevot, 1998), the sharp drop in Mrs(T) and NRM(T) curves is caused by the transitions of the domain state from a metastable configuration to a more stable one. These transitions are initiated by the processes of single- and heterophase oxidations of primary titanomagnetites under the laboratory heating of samples to moderate temperatures.

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