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Article Dans Une Revue Earth and Planetary Science Letters Année : 1992

Multicomponent magnetization in paleomagnetic records of reversals from continental sediments in Bolivia

Résumé

A paleomagnetic study of geomagnetic reversals has been attempted from three continental sections of the altiplano in Bolivia. The first section (Viscachani) shows a unique polarity interval with a magnetization carried by magnetite. In the two other sections (Achocalla and Irpavi) the magnetization is characterized by a complex magnetic mineralogy dominated by magnetic sulphides (mostly pyrrhotite) and magnetite. Thermal demagnetization performed under vacuum was found to be much more efficient than in air in isolating the directions of remanence carried by a low temperature (LT) component due to sulphides and a high temperature (HT) component due to magnetite. The directions of magnetization carried by the two minerals have been compared, with particular attention being paid to records of geomagnetic reversals. At Achocalla, the same polarity pattern is revealed by both components. However, the transitional directions of the LT component are located about 50 cm below the abrupt polarity change recorded by magnetite. Such observations are very similar to those from a recent study of Pliocene marine marl~ in Sicily [1]. These characteristics are compatible with the results of a simulation which assumed that a very early acquisition of the remanence was carried by the LT component and that a post-depositional reorientation of the magnetite occurred. In the last section (Irpavi), the observed LT and HT components have opposite polarities. Although the magnetic parameters indicate the presence of sulphides, we cannot rule out the hypothesis that the LT component has a secondary origin due to coarse magnetite grains. If we assume that the hypothesis of sulphides is correct, this observation emphasizes the difficulties in establishing the origin of sulphide minerals.

Dates et versions

hal-04013163 , version 1 (03-03-2023)

Identifiants

Citer

Xavier Quidelleur, Jean-Pierre Valet, Nicolas Thouveny. Multicomponent magnetization in paleomagnetic records of reversals from continental sediments in Bolivia. Earth and Planetary Science Letters, 1992, 111 (1), pp.23-39. ⟨10.1016/0012-821X(92)90166-S⟩. ⟨hal-04013163⟩

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