地球化学组成在不同粒级中的分布特征——以哈尔滨城市道路表土为例

The Distribution of Geochemical Composition in Different Grain-size Fractions: A Case Study of Road Surface Soils in Harbin City

将哈尔滨城市道路表土样品进行粒度分级,测定各粒级组分的常量元素、碳酸盐含量和碳酸盐碳同位素组成。结果显示,常量元素在不同粒级中的变化程度依次为:Al<Na<Si<K<Ca、Mg<Fe<Mn<P<Ti;Fe、Mg、Ca、Mn、Ti和P随粒度变细含量逐渐增加,而Si、Na和K元素则相反,Al元素与粒度的关系不清晰。化学风化指标按照以下的顺序受粒级的影响依次增大:CIA、(Al+Fe+Ti+Mn)/(Mg+Ca+K+Na)<(CaO+K2O+Na2O)/Al2O3<Fe2O3/MgO<K2O/Al2O3<(CaO+MgO+Na2O)/TiO2。碳酸盐含量在各粒级组分中变化幅度较大,且随着粒度的变细,碳酸盐含量逐渐增加。碳酸盐δ13C值在各粒级组分中的变化幅度较小,与粒级的关系较为复杂。

In the article, the samples of road surface soils in Harbin city are divided into different grain size fractions （bulk sample, 〉63 μm, 30-11 pan and 〈11 μm ） to measure major elements and carbonate and carbon iso- tope composition of different grain size fractions respectively. The results show that the variation degree of ma- jor elements in different grain size fractions is in sequence of AI〈Na〈Si〈K〈Ca, Mg〈Fe〈Mn〈P〈Ti, and the variation of A1 element is relatively stable. The volume of Fe, Mg, Ca, Mn, Ti and P elements gradually raise with decreasing grain size, while the volume of Si, Na and K is exactly the opposite.The relationship between A1 element and grain size is unclear, and A1 element is enriched in 〉63μm fraction, while the minimum in 63-30μm fraction. The influence of grain size to chemical weathering index is in sequence of CIA, （AI＋Fe＋Ti＋ Mn）/（Mg＋Ca＋K＋Na）〈（CaO＋K：O＋Na20）/AI：O3〈Fe203/MgO〈K20/A1203〈（CaO＋MgO＋Na20）/Ti02. The ratio of CIA and （AI＋Fe＋Ti＋Mn）/（Mg＋Ca＋K＋Na） is the best index reflecting the chemical weathering degree, and next is the ratio of （CaO＋K：O＋Na20）/AI：O3, Fe203/MgO and K20/Al2O3, and the influence of grain size to （CaO＋MgO＋Na20）/TiOz ratio is larger, resulting in that （CaO＋MgO＋Na20）/TiO2ratio is not a good index indi- cating chemical weathering degree of sediments. The variation range of carbonate volume in different grain size fractions is larger, and carbonate volume gradually raise with decreasing grain size, showing carbonate vol- umes are not a good indicator distinguishing dust source region. The variation range of carbon isotope compo- sition in different grain size fractions is less, showing carbonate carbon isotope compositions is a better tracing index indicating eolian dust provenance than carbonate contents, and the relationship between carbon isotope composition and grain size is relatively complicated, but most of samples are shown as ＂N shape＂ flexural vari- ation modes, namely, rises, then descends and again rises, with decreasing grain size.