黄土高原马兰黄土粘土矿物的定量研究

Quantitative Research on Clay Mineral Composition of the Malan Loessfrom the Loess Plateau in China

本文在回顾和总结中国西北黄土粘土矿物研究进展的基础上,提供了采用现代X-射线衍射(XRD)定量测试技术(包括粘土矿物样品处理和全自动数据处理技术)对陕北晋西12个县市马兰黄土粘土矿物定量研究的最新结果。测试结果表明,马兰黄土的主要粘土矿物为伊利石／蒙脱石混层矿物(相对含量为60％-70％),而不是以往所认为的伊利石。伊利石在黄土中主要呈两种形式存在,即单矿物伊利石和伊／蒙混层矿物中的伊利石。研究还发现,各地马兰黄土粘土矿物组成变化不大,但在神木、河曲、偏关一带伊／蒙混层比有局部增高的现象。根据扫描电子显微镜观察,黄土中粘土矿物不是以单粒形式存在,而主要是以集粒粘附物的形式包裹在碎屑颗粒表面。黄土中粘土矿物组成及其存在形式一方面可以充分揭示黄土物源区的表生化学环境特征;另一方面,伊／蒙混层矿物作为一种广泛分布的膨胀性粘土矿物和它在黄土粘土矿物中所占地位,对于认识马兰黄土在水作用下的湿陷变形和强度衰减的本质具有重要意义。

On the basis of a review of the research advances in the clay mineral composition of loess in China, the results of clay mineral composition, detected quantitatively by the method of X-ray diffraction including techniques of sample treatment and automatic data processing, of the Malan loess from 12 counties of northShaanxi and west Shanxi are reported in this paper. The quantitative analysis results indicate that the dominant clay mineral in the Malan loess is I/S mixed-layer mineral, and not illite as reported by former researchers. The illite in loess exists both in the form of single mineral and that of I/S mixed-layer mineral. It is discovered that the mineral composition of the Malan loess is similar in different zones, but the I/S mixed ratio is locally increased in Shenmu, Hequ and Pianguan counties. An observation by SEM indicates that the clay mineral particles do not exist in the form of single particles, either in the Malan loess or the Lishi loess, but appear as appendixes surrounding the debris surface, which can fully reveal the geochemical characteristics of the loess source area. Furthermore, as an important expansive clay mineral in loess, the I/S mixed-layer mineral can help us to understand the engineering properties of the Malan loess, such as collapse deformation and strength attenuation under the impact of water.