收稿日期: 2012-04-20
修回日期: 2012-05-21
网络出版日期: 2012-05-21
Geochemical Composition and Weathering Feature of Surface Sediment in the Dumeng Sandy Land, Northeast China
Received date: 2012-04-20
Revised date: 2012-05-21
Online published: 2012-05-21
本文分析了杜蒙沙地表土样品各粒级组分(全样、>63 μm、63~30μm、30~11 μm和<11 μm)的常量元素组成。结果表明:杜蒙沙地地表物质化学元素组成以Si、Al为主,与上地壳相比,除Si、Mn和Ti外,Fe、Mg、Ca和P严重亏损,Al和Na中度亏损,K轻微亏损;除Si、Al、Na、K外,Fe、Mg、Ca、Ti、P、Mn的变异系数均很高;常量元素在不同粒级中的变化程度按照Al<Si<Na<K<P<Fe<Ti<(Ca,Mn)<Mg的顺序依次递增,Al在不同粒级中的变化很小。Fe、Mg、Ca、Mn、Ti和P随着粒度的变细,含量逐渐增加,而Si、Na和K则相反,Al与粒度不存在明确的相关关系。化学风化指标按照CIA(化学蚀变系数)<(Al+Fe+Ti+Mn)/(Mg+Ca+K+Na)<(CaO+K2O+Na2O)/Al2O3<Fe2O3/MgO<K2O/Al2O3<(CaO+MgO+Na2O)/TiO2的顺序受粒度的影响依次增大, CIA是最好的化学风化指标,其次是(Al+Fe+Ti+Mn)/(Mg+Ca+K+Na)和(CaO+K2O+Na2O)/Al2O3,然后是Fe2O3/MgO和K2O/Al2O3,(CaO+MgO+Na2O)/TiO2比值受沉积物粒度的影响较大,不适合作为指示沉积物化学风化程度的指标。杜蒙沙地的CIA值为52.28,A-CN-K图解指示了杜蒙沙地处于化学风化的最初阶段,处于较弱的脱Ca、Na阶段,其他元素未发生明显化学风化或迁移;A-CNK-FM图解表明杜蒙沙地的Fe、Mg元素仅发生了微弱分异,原因在于半干旱、半湿润气候条件下杜蒙沙地微弱的机械风化,另外杜蒙沙地物质来源决定的短距离搬运也使Fe、Mg元素的分异不明显。
谢远云1 , 孟 杰1 , 郭令芬1 , 何 葵1 , 康春国2 . 松嫩平原杜蒙沙地地表物质的地化组成及风化特征[J]. 中国沙漠, 2013 , 33(4) : 1009 -1018 . DOI: 10.7522/j.issn.1000-694X.2013.00143
The surface sediment samples from Dumeng sandy land were collected and divided into different grain size fractions (bulk sample, >63 μm, 63-30 μm, 30-11 μm and <11 μm ). These samples were analyzed in the laboratory to obtain composition of geochemical elements. The result shows that Si and Al take up a large part of chemical composition of surface sediment in Dumeng sandy land. Compared with the average composition of geochemical elements in the upper continental crust (UCC), Fe, Mg and Ca are depleted to a severe degree, Al and Na are depleted to a medium degree, and K are depleted slightly; Fe, Mg, Ca, P, Ti and Mn contents have high coefficients of variation; The variation degrees of major elements in different grain size fractions increase in the following order: Al<Si<Na<K<P<Fe<Ti<(Ca, Mn)<Mg, and variation of Al element is relatively slight. The volumes of Fe, Mg, Ca, Mn, Ti and P elements gradually increase with decreasing grain size, while the volumes of Si, Na and K are exactly the opposite, and the relationship between Al element and grain size is not significant. The influence of grain size on chemical weathering index is ranked in the following order: CIA<(Al+Fe+Ti+Mn)/(Mg+Ca+K+Na)<(CaO+K2O+Na2O)/Al2O3<Fe2O3/MgO<K2O/Al2O3<(CaO+MgO+Na2O)/TiO2. CIA is the best index reflecting chemical weathering degree, and next are (Al+Fe+Ti+Mn)/(Mg+Ca+K+Na) and (CaO+K2O+Na2O)/Al2O3, followed by Fe2O3/MgO and K2O/Al2O3, and (CaO+MgO+Na2O)/TiO2 ratio is greatly influenced by grain size, so it isnt a good index of chemical weathering degree of sediments. The CIA value of Dumeng sandy land is 52.28, A-CN-K ternary diagram shows that these sediments are in the early stage of continental chemical weathering characterized by slight loss of Na and K, and other geochemical elements are in a less weathering or leaching process. A-CNK-FM ternary diagram suggests that Fe and Mg only have undergone slight chemical differentiation because of weak physical weathering and chemical weathering under the condition of semi-arid and semi-humid climatic. In addition, short transport distance of sediments in Dumeng sandy land makes Fe and Mg differentiation not obvious.
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