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Effect of Single-Phase Oxidation of Titanomagnetite in Basalts on the Determination of Intensity and Direction of Paleomagnetic Fieldстатья
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Дата последнего поиска статьи во внешних источниках: 11 мая 2022 г.
- Авторы: Maksimochkin V.I., Grachev R.A., Tselebrovskiy A.N.
- Журнал: Izvestiya. Physics of the Solid Earth
- Том: 58
- Номер: 2
- Год издания: 2022
- Издательство: Pleiades Publishing, Inc.
- Местоположение издательства: New York, USA
- Первая страница: 216
- Последняя страница: 229
- DOI: 10.1134/S1069351322020070
- Аннотация: We present the results of studying the effect of laboratory oxidation of titanomagnetite in P72/4basalt from the Red Sea rift zone, which carries natural remanent magnetization (NRM), on the preservationof the paleomagnetic signal. To simulate the in situ titanomagnetite oxidation, basalt samples were annealedat temperature Tan = 260°C in the magnetic field with Ban = 50 μT during 0–1300 h. It is shown that underannealing in air, single-phase oxidation of titanomagnetite takes place: after annealing during 1300 h, themedian Curie temperature (Тс) has increased from 260 to 435°C. The subsequent heating to 600°C in argonleads to the homogenization of the oxidized titanomagnetite. The presence of single-phase oxidized titanomagnetitegrains in basalts can be diagnosed by comparing Тс of the sample in the initial state and afterhomogenization, and the difference of these temperatures is a measure of the degree of oxidation. It is establishedthat single-phase oxidation of titanomagnetite in magnetic field leads to the acquisition of magnetization with blocking temperatures above Тс of the initial state; its contribution to the total magnetization increases with increasing annealing time. The Arai-Nagata diagrams based on the results of the Thellier experiments characteristically have a bend at T ≈ 360°С for all annealing times (12.5–1300 h). The intensityof the paleomagnetic field (Bcalc) calculated in the temperature interval 260–360°C from the remanent magnetization of basalt titanomagnetite single-phase oxidized in the laboratory experiment is by 25–30% lower than that estimated from the initial NRM, irrespective of the degree of oxidation, and, within the error, is equal to the field acting during the annealing. In the case of low degree of oxidation (Z ∼ 0.3) after 100 h ofannealing, the direction of the initial NRM can only be reconstructed from the results of thermal demagnetization.At long exposure times (t = 400 and 1300 h) and high oxidation degree Z = 0.35–0.69, the directionof the initial NRM cannot be reconstructed by any of thermal demagnetization methods.
- Добавил в систему: Максимочкин Валерий Иванович