Effect of Aspect on Weathering Rates and Clay Mineralogy of Soils Developed on Andesite/Trachyandesite Parent Materials under Semi-Arid Conditions

In this study a soil sequence was investigated on North and South facing slopes with respect to elemental balances (Ca, Mg, K, Na, Si, Al, and Fe) and the occurrence and abundance of clay minerals. Elemental losses were derived from mass balance calculations that are based on enrichment/depletion factor by taking the immobile element content (titanium, Ti) as reference and using some weathering indices such as Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), bases/R_2O_3 ratio, Plagioclase Index of Alteration (PIA), and Product Index (P). According to the indices used for the interpretation of the degree of weathering in parent materialin 4 profiles were found to be low in accordance to the age of the geological parent material. Higher values of the mass balance functions and mass loss/gain budget in profiles situating in southern part of the hill have indicated the importance of stending in the degree of weathering. The intensity and abundance of K-feldspar and quartz was higher in northern hill sites and this indicated that the weathering processes may considerably change in short distances. Smectites and interlayered smectites-illite clay minerals were observed in southern hill whereas the soils of northern hill consisted of illite, kaolinite, and smectites in descending order. It can be concluded that the differences in concentration of major element in a profile and clay mineralogy in short rages may quantify the effect of topolithosequence.