黔北白云岩红色风化壳元素地球化学特征

Element geochemical characteristics of red weathering crust from dolomite,north Guizhou,China

选取贵州高原喀斯特地区典型白云岩风化剖面作为研究对象,探讨了红土剖面元素迁移特征及其影响因素,为进一步认识红色风化壳元素地球化学特征提供依据。结果表明：（1）红土剖面中土壤样品（XPS-4~XPS-25）Fe、K、Mn常量元素及Co、Pb、Zn微量元素的分布曲线相对于其他元素靠近UCC,元素Mg、Ca、Na、Ti和Li、Cr、Ba、V的数据点则显著偏离了上部陆壳的平均组成。（2）元素对协变分析得出Ti与Fe、Ba和V的积累特征一致,呈增加趋势;Ti与Mg呈反向变化特征。（3）以Ti为参比元素的剖面迁移特征表明,绝大部分元素的地球化学行为表现为迁移淋失,仅Fe、Cr和V富集。K、Ba总体上呈迁出趋势,个别层段有轻微富集;Na和Co在风化原岩处有一个富集端点。元素在风化过程中的迁移聚集与土壤剖面的pH值和剖面结构变化、粘土矿物和有机质等的吸附有关。

The Guizhou plateau is in the eastern part of the Yunnan-Guizhou plateau,where variable karst landscapes are widely distributed.A typical dolomite weathering profile from a karst area with a subtropical humid monsoon environment was selected for study of the behavior of major and trace elements in northern Guizhou province,China.The transport function and factors affecting fourteen major and trace elements were analyzed.The elemental Fe,Mg,Ca,Na,Ti,K,Mn,Li,Cr,Co,Ba,V,Pb,and Zn content of 25 strata were determined.A mass transport calculation is presented which was employed as a method to determine the mobility of those elements during each stage in a progressive geochemical process and then used to calculate the gain or loss of each element during the whole process.It is possible to provide a systematic basis for the geochemical characters of elements in the red weathering crust.In order to achieve these goals,efficient approaches were employed,including field investigation,laboratory testing and data analysis.It was determined that,（1）Relative to the other elements,the average contents of Fe,K,Mn and Co,Pb,Zn are,in general,similar to UCC values during weathering.In contrast,values for Mg,Ca,Na,Ti and Li,Cr,Ba,V deviate greatly from UCC,with some abnormal values（XPS-4to XPS-25）.（2）Ti-Fe,Ti-Ba and Ti-V indicate the same increasing chemical weathering trend.Conversely,Ti-Mg has a negative trend during the whole weathering of dolomite.（3）Taking Ti as the reference and compairing element for calculation,mass-balance equations were applied to geochemical analyses to show that most of the elements had migrated and leached,while Fe,Cr and V were enriched during the chemical weathering process.Likewise,elements such as K and Ba had migrated and leached,but were slightly enriched in some layers of the weathering profile.Na and Co were enriched in the weathering protolith.This enrichment may have been caused by both the biogeochemical process and changes in pH and sectional structure,as well as the adsorption of elements by clay minerals and organic materials during chemical weathering.