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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Characteristics and genesis of maghemite in Chinese loess and paleosols: Mechanism for magnetic susceptibility enhancement in paleosols
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Characteristics and genesis of maghemite in Chinese loess and paleosols: Mechanism for magnetic susceptibility enhancement in paleosols

机译：黄土和古土壤磁赤铁矿的特征与成因：古土壤磁化率增强的机理

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摘要

Morphological characteristics and microstructures of magnetic minerals extracted from Chinese loess and paleosols were investigated using powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), Our results indicate that maghemite in loess-paleosol sequences was transformed from magnetite through oxidation of magnetite. Maghemite transformed from eolian magnetite during chemical weathering has low-angle grain boundaries among maghemite nano-crystals. Some nano-crystalline maghemites with nanoporous texture resulted from microbe-induced precipitation of magnetite or transformation of poorly crystalline ferric Fe (oxy)hydroxides in presence of Fe-reducing bacteria. Aggregates of euhedral maghemite nanocrystals were transformed from magnetite magnetosomes. Both microbe-induced nanoporous magnetite and microbe-produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols. It is proposed that the formation of nano-crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility, although the total amount (weight percent) of magnetic minerals in both paleosol and loess units is similar. Our results also show that nano-crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi-arid soil environments instead of hematite, although hematite is a thermodynamically stable phase, This result also indicates that a decrease in crystal size will increase stability of maghemite. It is also inferred that surface energy of maghemite is lower than that of hematite. (C) 2005 Elsevier B.V. All rights reserved.
机译：利用粉末X射线衍射（XRD）和高分辨率透射电子显微镜（HRTEM）研究了黄土和古土壤中磁性矿物的形态特征和微观结构，研究结果表明黄土古土壤中的磁赤铁矿是通过磁铁矿转化为黄铁矿的。磁铁矿的氧化。在化学风化过程中从风成磁铁矿转变而来的磁赤铁矿在磁赤铁矿纳米晶体之间具有低角度的晶界。一些具有纳米孔结构的纳米晶磁赤铁矿是由于微生物引起的磁铁矿沉淀或在还原铁细菌的存在下结晶性较差的三价铁（羟基）氢氧化物的转化而产生的。从磁铁矿磁小体转化了本性磁赤铁矿纳米晶体的聚集体。微生物诱导的纳米多孔磁铁矿和微生物产生的磁铁矿磁小体都与微生物活性和古土壤的成岩作用直接相关。尽管在古土壤和黄土单元中磁性矿物的总量（重量百分比）相似，但建议在古土壤中形成具有超顺磁性的纳米晶磁赤铁矿会提高磁化率。我们的结果还表明，尽管赤铁矿是热力学稳定的相，但纳米晶体和纳米多孔磁铁矿晶粒更倾向于在半干旱土壤环境中转变为磁赤铁矿，尽管赤铁矿是热力学稳定的相。该结果还表明，减小晶体尺寸将增加磁赤铁矿的稳定性。还可以推断，磁赤铁矿的表面能低于赤铁矿的表面能。 （C）2005 Elsevier B.V.保留所有权利。

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