中国黄土的平均化学成分:上部大陆地壳的一种典型代表

本文通过对黄河中游地区马兰黄土的大面积野外实地考察,系统采样和室内分析测试,并采用质量加权平均的计算方法,给出了较为准确的中国黄土平均化学成分数据。中国黄土相对于下地壳和全地壳较富大离子半径的亲石元素而贫亲铁元素;与上部大陆地壳相比,中国黄土除相对较富Ca、B而贫Na、Nb外,其余绝大多数化学元素的丰度均非常接近甚至几乎相等。由此表明,中国黄土确属典型的上部大陆地壳物质,它不仅为暴露的上部大陆地壳提供了一种理想的天然平均样品,而且中国黄土的平均化学成分完全可以作为上部大陆地壳化学成分的代表而加以应用。

AVERAGE CHEMICAL COMPOSITION OF LOESS IN CHINA: AS A GOOD REPRESENTATIVE OF THE UPPER CONTINENTAL CRUST

The average chemical composition of loess in China has been measured and calculated by the method of mass-welghted average calculation on the basis of extensive sampling and labora-tory chemical analysis. Great differences are noticed in chemical composition between loess of China and the lower or the bulk crust,the former being characterized by the relative enrichment of LIL elements and the latter two by the enrichment mainly of siderophile elements. Much si-milarity is indicated in chemical composition between loess of China and the upper crust. In addi-tion to the enrichment of Ca and B and the depletion of Na and Nb,the majority of the other ele-ments in the loess of China show little or, even no difference in contents from those in the upper crust. The above charaeterisitics indicate tha loess of China typically belongs to upper crustal material. Loess of China not only provides a kind of ideal natural average samples of the exposed upper continental crust,but also can be used,if its average chemical composition is taken into consideration,to represent the chemical composition of the upper continental crust.