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.

中文翻译：

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亚铁磁性晶粒的单相氧化是 L 形 Arai-Nagata 图的一个原因

摘要——2006 年在亚美尼亚东北部采集的 Berd（侏罗纪）和 Paravakar（白垩纪）玄武岩中，通过 Thellier 法测定地球磁场古强度 Banc 的实验揭示了 Arai-Nagata 图的异常行为。该异常表现为在将样品加热至约 400°C 时自然剩磁 (NRM) 的强度急剧下降，同时在此温度区间内获得的部分热剩磁 (pTRM) 非常微弱。温度的进一步升高会导致相反的现象——pTRMs 强度出乎意料地急剧上升，而 NRM 几乎没有下降，这产生了 Arai-Nagata 图的 L 形。对于剩余饱和磁化强度 Mrs(T) 也建立了类似的热退磁过程中急剧下降的现象。我们进行了许多磁矿物学实验，从中我们得出的结论是，与 (Kosterov and Prevot, 1998) 提出的假设一致，Mrs(T) 和 NRM(T) 曲线的急剧下降是由域的转变引起的状态从亚稳态配置到更稳定的配置。这些转变是由初级钛磁铁矿在实验室加热至中等温度下的单相和异相氧化过程引发的。Mrs(T) 和 NRM(T) 曲线的急剧下降是由域状态从亚稳态配置到更稳定配置的转变引起的。这些转变是由初级钛磁铁矿在实验室加热至中等温度下的单相和异相氧化过程引发的。Mrs(T) 和 NRM(T) 曲线的急剧下降是由域状态从亚稳态配置到更稳定配置的转变引起的。这些转变是由初级钛磁铁矿在实验室加热至中等温度下的单相和异相氧化过程引发的。