亚热带富铁土的磁学性质及其磁性矿物学

MAGNETIC PROPERTIES OF SUBTROPICAL FERRISOLS AND ITS MAGNETIC MINERALOGICAL STUDY

通过５５个亚热带富铁土的磁化率（χ）、频率磁化率（χ_（ｆｄ））、非滞后剩磁（ＡＲＭ）和饱 和等温剩磁（ＳＩＲＭ）等磁性参数测定，结合氧化铁化学形态分析和矿物鉴定，初步明确了亚热 带富铁土的磁学特征及其磁性矿物．磁测数据表明富铁土中存在强磁性的矿物，其磁化率χ 与土壤游离氧化铁（Ｆｅ_ｄ）含量呈极显著指数正相关（Ｒ~２＝０．５９７１），频率磁化率χ_（ｆｄ）与土壤游离氧 化铁含量呈极显著直线正相关（Ｒ~２＝０．４２８９）．富铁土的χ_（ｆｄ）和非滞后磁化率χ_（ＡＲＭ）。值表明土壤 中的磁性矿物以超顺磁性（ＳＰ）和稳定单畴（ＳＳＤ）颗粒为主，富铁上的χ和χ_（ＡＲＭ）呈极显著直线 正相关（Ｒ~＝ ０．９４２９），证明富铁土的磁性是由风化成土过程产生的 ＳＰ和 ＳＳＤ磁性颗粒贡献 的．矿物磁测结合Ｘ－衍射证明富铁土中的氧化铁矿物由赤铁矿、磁赤铁矿和针铁矿组成。

Mineral magnetic parameters, such as magnetic susceptibility (χ ), frequency dependent susceptibility (χ_(fd) ), anhysteretic remanent magnetization (ARM and saturation isothermal remanent magnetization (SIRM), were measured on 55 samples of Ferrisols selected from Quaternary red clay in subtropical regions of China. The measurement data, in combination with chemical selective dissolution of iron oxide and X-ray diffraction analysis, provide insight into the magnetic characteristics and magnetic mineralogy of Ferrisols. Results show that strong magnetic minerals were found in most of the Ferrisols. The χ values of Ferrisols have highly significant exponential positive correlation with free iron oxide (Fe_d) contents of soils (R^2 = 0.5971), and χ_(fd) values have highly significant linear correlation with Fe_d contents of soils (R^2 = 0.5971). The χ_(fd) and ARM susceptibility (χ_(ARM) ) values of Ferrsols imply that the magnetic minerals in the soils exist mainly in superparmapnetic (SP) / stable single domain (SSD) grain sizes. The χ values are positively proportional to χ_(ARM) of soils (R^2 = 0.9429), indicating that the magnetism of Ferrisols mainly come from the contribution of pedogenic SP and SSD magnetic grains. Mineral magnetic measurements and X-ray diffraction pattern indicate that iron oxide mineralogy of Ferrisols is comprised of hematite (α-Fe_ 2 O_3), maghemite (γ-Fe_ 2 O_3) and goethite (α-FeOOH), suggesting that maghemite is the main magnetic minerals in Feinsols. Possible mechanism of origin of maghemite in Ferrisols is discussed.