Transformation relationship among different magnetic minerals within loess-paleosol sediments of the Chinese Loess Plateau  

作　　者：XIE QiaoQin CHEN TianHu XU XiaoChun QING ChengSong XU HuiFang SUN YuBing JI JunFeng 

机构地区：[1]School of Natural Resources and Environment,Hefei University of Technology,Hefei 230009,China [2]Department of Geology and Geophysics,University of Wisconsin,Madison WI 53706,USA [3]Institute of Surficial Geochemistry,State Key Laboratory of Mineral Deposits Research,Department of Earth Sciences,Nanjing University,Nanjing 210093,China

出　　处：《Science China Earth Sciences》2009年第3期313-322,共10页中国科学（地球科学英文版）

基　　金：Supported by National Natural Science Foundation of China (Grant Nos. 40772032 and 40573054);National Basic Research Program (Grant No. 2007CB815603)

摘　　要：The dominant magnetic minerals and carriers of magnetic signals within the Chinese Loess Plateau are magnetite, maghemite, hematite, and goethite. In this study, we investigated the provenance and evo- lution of magnetic minerals during loess pedogenesis, using X-ray diffraction (XRD) and optical and electron microscopy, including field emission scanning electron microscopy (FESEM) and high- resolution transmission electron microscopy (HRTEM). Our results reveal that single- and multiphase mineral assemblages among magnetic minerals in the loess-paleosol sequence have been formed. Partial oxidation of coarse eolian magnetite has occurred in the desert source area and the oxidation degree is enhanced after deposition of the dust upon the Chinese Loess Plateau. This mode of origin resulted in a microtexture consisting of an inner magnetite core surrounded by a hematite rim, and strongly affected the magnetic characteristics of the loess. Goethite coexists with hematite in the loess and paleosol, and nanometer-scale hematite is formed upon goethite rims via dehydration. Our study provides direct mineralogical evidence of the magnetic record and paleoclimatic implications of the loess–paleosol sequence of the Chinese Loess Plateau.The dominant magnetic minerals and carriers of magnetic signals within the Chinese Loess Plateau are magnetite, maghemite, hematite, and goethite. In this study, we investigated the provenance and evolution of magnetic minerals during loess pedogenesis, using X-ray diffraction (XRD) and optical and electron microscopy, including field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Our results reveal that single- and multiphase mineral assemblages among magnetic minerals in the loess-paleosol sequence have been formed. Partial oxidation of coarse eolian magnetite has occurred in the desert source area and the oxidation degree is enhanced after deposition of the dust upon the Chinese Loess Plateau. This mode of origin resulted in a microtexture consisting of an inner magnetite core surrounded by a hematite rim, and strongly affected the magnetic characteristics of the loess. Goethite coexists with hematite in the loess and paleosol, and nanometer-scale hematite is formed upon goethite rims via dehydration. Our study provides direct mineralogical evidence of the magnetic record and paleoclimatic implications of the loess-paleosol sequence of the Chinese Loess Plateau.

关 键 词：Chinese LOESS-PALEOSOL SEQUENCE magnetic MINERALS phase RELATIONSHIPS MINERALOGY 

分 类 号：P575[天文地球—矿物学]