不同水热条件下玄武质火山碴发育土壤的形态学和矿物学特征比较

Morphological and Mineralogical Characteristics of Basaltic Volcanic Ballast Soils under Different Hydrothermal Conditions

自半干旱地区和湿润地区选取发育于玄武质火山碴、且成土时间和地形等条件相近的土壤剖面,通过比较其形态学、矿物学特征,探讨不同水热条件对该类土壤发生发育的影响。结果表明:(1)发育于半干旱地区的土壤土体内石砾碴块含量大于湿润地区,其粒径<2 mm的细土部分质地多为砂质壤土和砂土,而发育于湿润地区的质地多为壤土。(2)发育于半干旱地区的土壤粒径2~0.5 mm和0.5~0.25 mm的砂粒风化程度较低,呈棱角状,其上气孔肉眼清晰可见;而湿润地区该粒级砂粒呈次棱角或次圆状,其上气孔肉眼模糊难辨。(3)发育于玄武质火山玻璃的土壤均有脱玻化过程发生,石英含量自表层向下层逐渐减少;但分布于半干旱地区的仅0.5~0.25 mm和0.25~0.1 mm粒级砂粒中有石英出现,而湿润地区土壤2~0.5 mm、0.5~0.25mm、0.25~0.1 mm三个粒级砂粒中均有石英矿物存在;有石英出现的相同粒级比较,分布于湿润地区土壤砂粒中石英含量高于半干旱地区土壤。(4)湿润地区土壤中含有较多的伊利石、高岭石、蛭石、羟基铝蛭石和埃洛石等结晶质黏土矿物,而分布于干旱地区的土壤中则不含或含少量结晶质黏土矿物。

Basaltic volcanic ballast soil profiles with similar forming time and geographical condition were selected from the semi-arid and humid regions. The effect of hydrothermal conditions on soil development was investigated by comparing the morphological and mineralogical characteristics of basaltic volcanic ballast soils. The results showed that:(1) The content of gravel in the soils in the semi-arid region was higher than that in the humid region. The texture of fine soil(size < 2 mm) mainly was sandy loam and sandy in the semi-arid region, and was loam in the humid region.(2) The 2-0.5 mm and 0.5-0.25 mm sand granules developed in the semi-arid region were slightly weathered, with visible holes. They were subangular or subcircular in the humid region, with barely holes.(3) Soil derived from basaltic volcanic glass experienced devitrification, and the quartz content decreased with the increase of soil depths. The quartz minerals only were found in 0.5-0.25 mm and 0.25-0.1 mm sand in the semi-arid region,but in 2-0.5 mm, 0.5-0.25 mm and 0.25-0.1 mm fractions in the humid region. And the quartz content in the same size sand was higher in the humid region than that in the semi-arid region.(4) There were many crystalline clay minerals such as illite, kaolinite, vermiculite, hydroxyl-aluminum vermiculite, and halloysite in soils in the humid regions, while no or small amount of crystalline clay minerals was detected in soils in the arid regions.