GJI Geomagnetism, rock magnetism and palaeomagnetism Temperature dependence of magnetic susceptibility in an argon environment: implications for pedogenesis of Chinese loess/palaeosols
GJI Geomagnetism, rock magnetism and palaeomagnetism Temperature dependence of magnetic susceptibility in an argon environment: implications for pedogenesis of Chinese loess/palaeosols
复制标题
DOI：
--
复制
发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Qingsong Liu;C. Deng;Yongjae Yu;M. Jackson;Subir K. Banerjee;Rixiang Zhu
中科院分区：
文献类型：
--
作者：
Qingsong Liu;C. Deng;Yongjae Yu;M. Jackson;Subir K. Banerjee;Rixiang Zhu
磁化率（χ − T）的温度依赖性已被广泛用于确定天然样品在热处理过程中的矿物学变化。我们进行了综合岩石磁性实验来解释中国黄土/古土壤在氩气中的χ-T曲线。我们使用原材料和加热样品。此外，我们还研究了磁性提取物和残留物的磁性，以量化每个馏分对整体磁性的贡献。在加热曲线中，磁化率损失（约30%）在300 - 400千居里之间，是由成土细粒磁赤铁矿向赤铁矿的转化引起的，这表明磁化率损失可以作为中国黄土/古土壤中成土细粒超顺磁性（SP）颗粒浓度的一个新指标。与升温曲线不同，冷却曲线主要由新形成的细粒磁铁矿主导，主要尺寸为35 nm。这些细粒磁性颗粒的新产物的开始发生在400 ℃。有趣的是，经过700 ° Cr处理后加热的样品的室温磁化率（χ ph）与成土作用的程度无关，并在约33 - 35 × 10 - 7 m 3 kg-1时饱和，这表明磁化率的增强仅受控制加热过程中含铁风成矿物的还原。看来，在氩气中进行的700 ℃热处理在某种意义上可能与成土过程类似。因此，我们预测，成土作用可以为末次间冰期古土壤单元（S1）产生的最大磁化率为33 - 35 × 10 −7 m3 kg −1。在实际应用中，χ ph可用于定量黄土高原的风沙输入。
SUMMARY 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 ◦ Ci scaused 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 finegrained magnetic particles occurs at ∼400 ◦ C. It is interesting that the room-temperature magnetic susceptibility (χ ph )o fthe samples heated after a 700 ◦ Cr un is independent of the degree of pedogenesis and saturates at approximately 33‐35 × 10 −7 m 3 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 m 3 kg −1 is the maximum susceptibility that pedogenesis can generate for the last interglacial palaeosol unit (S1). In practice, χ ph would be useful to quantify the aeolian inputs to the Chinese Loess plateau.