引起红土表层硅铝比值增大原因的可能性探讨

Si/Al或SiO2 /R2 O3 常常作为表生化学风化作用强度的重要指标。随着化学风化作用的进行 ,硅铝比或硅铝铁率表现出逐渐降低的演化趋势。中国南方的红土风化壳 ,是强烈化学风化作用的产物 ,被认为处于或经历了脱硅富铝化阶段。但是在红土剖面上部常常出现该比值不降反升的现象 ,给运用这一指标指示化学风化强度带来了困难。通过对贵州平坝、新蒲及花溪碳酸盐岩红色风化壳化学风化程度的研究 ,以及对中国南方几种不同结晶母岩上发育的红土的化学风化强度指标的对比讨论 ,探讨了产生这种现象的可能性原因。指出Fe、Al氧化物的下渗和淋失作用及其硅质的相对富集是引起中国南方红土表层出现Si/Al和SiO2 /R2 O3升高的主要原因。

DISCUSSION ON POSSIBLE CAUSES OF INCREASES IN Si/Al RATIO IN SURFACE LAYERS OF SOME LATERITIC PROFILES

The ratios of SiO 2/Al 2O 3 or SiO 2/R 2O 3 are usually used as indices of supergene chemical weathering intensity. With chemical weathering processing, the ratios of SiO 2/Al 2O 3 or SiO 2/R 2O 3 tend to decrease gradually. But those of lateritic weathering crusts in southern China tend to increase, bringing about difficulties to indicate the chemical weathering intensity. This paper probed into the possible causes for this abnormal phenomenon in terms of the chemical weathering degree of lateritic weathering crusts of dolomitite at Pingba, Xinpu and Huaxi, and discussed some lateritic weathering crusts of different mother rocks in southern China. It is pointed out that increases in ratios of SiO 2/Al 2O 3 or SiO 2/R 2O 3 are attributed to leaching and infiltration of oxides of Fe and Al, and relative enrichment of quartz.