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Temperature dependence of magnetic susceptibility in an argon environment: implications for pedogenesis of Chinese loess/palaeosols

2005; Oxford University Press; Volume: 161; Issue: 1 Linguagem: Inglês

10.1111/j.1365-246x.2005.02564.x

1365-246X

Qingsong Liu, Chenglong Deng, Yongjae Yu, J. Torrent, Mike Jackson, Subir K. Banerjee, Rixiang Zhu,

Geochemistry and Elemental Analysis

Temperature dependence of magnetic susceptibility (χ−T) has been widely used to determine changes in mineralogy of natural samples during heat treatment. We carried out integrated rock magnetic experiments to interpret the χ−T curves of the Chinese loess/palaeosols in argon. We used both raw materials and heated samples. In addition, we also investigated the magnetic properties of magnetic extracts and residues to quantify contributions from each fraction to the bulk magnetic properties. For the heating curves, the susceptibility loss (∼30 per cent) between ∼300–400 °C is caused by the inversion from pedogenic fine-grained maghemite to haematite, suggesting that the susceptibility loss can be used as a new concentration index of the pedogenic fine-grained superparamagnetic (SP) particles in the Chinese loess/palaeosols. Unlike the warming curves, the cooling curves are dominated by newly formed fine-grained magnetites with a dominant size of ∼35 nm. The onset for the new production of these fine-grained magnetic particles occurs at ∼400 °C. It is interesting that the room-temperature magnetic susceptibility (χph) of the samples heated after a 700 °C run is independent of the degree of pedogenesis and saturates at approximately 33–35 × 10−7 m3 kg−1, indicating that the susceptibility enhancement is controlled only by the reduction of Fe-bearing aeolian minerals during heating. It appears that the 700 °C thermal treatment in argon could be in some sense an analogue to the pedogenic processes. Thus, we predict that ∼33–35 × 10−7 m3 kg−1 is the maximum susceptibility that pedogenesis can generate for the last interglacial palaeosol unit (S1). In practice, χph would be useful to quantify the aeolian inputs to the Chinese Loess plateau.