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本文对发育于花岗岩上的两个亚热带红土剖面进行了系统的岩石磁学研究,测试了磁化率、频率磁化率、等温剩磁、非磁滞剩磁、磁滞回线等常温磁学参数,选取代表性样品进行了高低温岩石磁学分析,拟探讨亚热带红土磁性矿物的特征及湿热环境下土壤中磁性矿物的转化规律。实验结果表明:亚热带红土的强磁性矿物为磁铁矿、磁赤铁矿;弱磁性矿物为赤铁矿和针铁矿,滞水土层中含有纤铁矿。花岗岩具有较强的磁性,在其上发育的红土也因此具有较强的磁性。花岗岩中的亚铁磁性矿物的磁畴以多畴占主导地位,随着风化强度的增强,逐渐形成较细粒的超顺磁与单畴磁性矿物。亚热带红土中的磁赤铁矿与位于半干旱区黄土高原成土作用形成的磁赤铁矿存在着磁学性质上的差异,表现为具有更高的居里点(约600℃和640℃),可能说明亚热带红土中的磁赤铁矿粒径更粗。两个剖面在磁学性质上存在着明显的差异,泉州剖面磁性矿物以磁铁矿为主,磁化率最高可达1823×10~(-8)m~3/kg,平均值为1033.1×10~(-8)m~3/kg,具有较低的剩磁矫顽力;福州剖面磁性矿物以磁铁矿和部分热稳定磁赤铁矿为主,磁化率最高为385.73×10~(-8)m~3/kg,平均值为91.5×10~(-8)m~3/kg。基于磁学参数分析,认为母质与后期成土作用共同造成了两个剖面的磁学性质差异,但后者起主导作用。磁化率在两个剖面中,均随着深度减小而减小,与温带地区表层土磁化率增强有很大区别。湿热环境条件下,强磁性矿物溶解或转化为弱磁性矿物的程度主导剖面磁化率变化。
In this paper, we systematically studied the rock magnetism of two subtropical red clay profiles developed on granite. The magnetic parameters such as magnetic susceptibility, frequency susceptibility, isothermal remanence, non-hysteresis remanence and hysteresis loop were measured. A representative sample was selected for magnetic analysis of high and low temperature rocks. The characteristics of magnetic minerals in subtropical red clay and the transformation rules of magnetic minerals in soils under wet and hot conditions were discussed. The experimental results show that the ferromagnetic minerals in the subtropical red soil are magnetite and maghemite, the weak magnetic minerals are hematite and goethite, and the hydrothermal reservoirs contain lepidocrocite. Granite has a strong magnetic, red clay in the development of it therefore has a strong magnetic. The magnetic domains of ferrimagnetic minerals in granite are dominated by multi-domains, and the more finely-grained superparamagnetic and monodomain magnetic minerals gradually form with the enhancement of weathering intensity. There are differences in magnetic properties between maghemite in subtropical red clay and magmatic hematite formed in the loess plateau by semi-arid region, showing higher Curie point (about 600 ℃ and 640 ℃) , May indicate that the magnetic hematite in subtropical red clay particle size coarser. There are obvious differences in the magnetic properties of the two sections. The magnetite in Quanzhou section is mainly magnetite with the highest magnetic susceptibility of 1823 × 10 ~ (-8) m ~ 3 / kg with an average of 1033.1 × 10 ~ (-8) m ~ 3 / kg, with lower remanence coercivity. The magnetic minerals in Fuzhou section are mainly magnetite and some thermostable maghemite with the highest magnetic susceptibility of 385.73 × 10 ~ (- 8) m ~ 3 / kg, with an average of 91.5 × 10 ~ (-8) m ~ 3 / kg. Based on the analysis of magnetic parameters, it is considered that the magnetic properties of the two sections are caused by the parent material and later soil-forming, but the latter plays a leading role. The magnetic susceptibility decreases in both sections with decreasing depth, which is greatly different from that in the temperate zone. Under wet and hot environmental conditions, the change of magnetic susceptibility of the dominant profile is the extent to which the ferromagnetic minerals dissolve or transform into weakly magnetic minerals.