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位于我国热带、亚热带地区的南方红土是我国分布最广的第四纪土状沉积,其经历了较强的化学风化作用,具有典型的磁性矿物组成。磁性矿物是沉积物的重要组成成分。磁性矿物的种类、粒度和含量等信息可以反映沉积物形成时的温度、降水等气候条件。因此,了解红土沉积物磁性矿物组成对于研究南方红土区的环境演化具有重要意义。本文综合分析了安徽宣城、浙江长兴、江西九江及广西百色4个剖面不同层位红土样品的x-T曲线、三轴等温剩磁热退磁曲线等岩石磁学结果,发现南方红土的磁性矿物组成主要为磁铁矿、磁赤铁矿、赤铁矿及针铁矿,这些磁性矿物的相对含量不仅具有地带性差异,而且在不同风化阶段也存在差异。其中百色剖面顶部棕色土中磁赤铁矿含量相对其他剖面较高,与百色地区现今较强的风化作用相符。同一剖面内网纹红土中赤铁矿的含量较高,磁赤铁矿的含量相对较低,指示网纹化时期较强的成土作用引起磁赤铁矿向赤铁矿的转化。此外,岩石磁学结果显示百色剖面网纹红土及均质红土中含有一种特殊性质的磁性矿物,即粒度较细、解阻温度较低的成土成因赤铁矿,该矿物为后期强烈风化作用的产物。该次生矿物携带了较强的化学剩磁,引起了百色剖面初始碎屑剩磁的重磁化。该研究表明磁性矿物组成的差异还可以用来解释南方红土剩磁记录的多样性。
The southern laterite, located in the tropical and subtropical regions of China, is the most widely distributed Quaternary earth-like sediment in China. It experienced strong chemical weathering and has typical magnetic minerals. Magnetic minerals are important components of sediments. Magnetic minerals, such as the type, size and content of sediment can reflect the formation of temperature, precipitation and other climatic conditions. Therefore, understanding the composition of magnetic minerals in lateritic sediments is of great significance for studying the environmental evolution in the laterite area. In this paper, xT curves and triaxial isothermal remanent magnetothermal demagnetization curves of red earth samples from four layers of Xuancheng, Changxing, Zhejiang, Jiujiang, Jiangxi and Baise, Guangxi were analyzed. It is found that the main mineral components of the lateritic clay For the magnetite, maghemite, hematite and goethite, the relative content of these magnetic minerals not only have a zonal difference, but also in different weathering stages are also different. The content of maghemite in brown soil at the top of Baise section is higher than other sections, which is consistent with the strong weathering in Baise today. In the same profile, the content of hematite in reticulate red soil is relatively high, and the content of maghemite is relatively low, which indicates that the stronger soil formation during reticulation period leads to the conversion of maghemite to hematite. In addition, the rock magnetism results show that the Baise profile reticulate red clay and the homogeneous laterite contain a special type of magnetic minerals, namely, the smaller size and the lower the temperature of deblocking, the hematite-forming hematite, which is strongly weathering later The product of action. The secondary minerals carry a strong chemical remanence, causing the remanent remanence of the initial detritus in the Baise section. The study shows that differences in the composition of magnetic minerals can also be used to explain the diversity of remanence records in the lateritic red earth.