Regolith profiles developed from a granitic parent rock in a sub-humid climate: implications for pedogenesis and chemical mobility of elements

Regolith profiles develop as a result of weathering of the parent rocks under varying climatic conditions, and weathering trends and mobility of various elements vary according to the parent rocks and climatic conditions. In the present study, regolith profiles developed from a granitic rock near Khajuraho town of central India are investigated to understand the nature of pedogenesis, weathering trend and the mobility of different elements under a sub-humid climatic condition. The regolith profiles show the dominance of oxidation process with the occurrence of clay and ferruginous coatings around the skeletal grains. They contain quartz, K-feldspars, and albite, besides clay minerals in the upper horizons. The regolith profiles show more mobility of Si and Na, which are depleted in the regolith profiles in comparison to the parent rock. The TiO2 vs. SiO2 plot shows strong negative correlation, while the TiO2 vs. Na2O plot shows weak negative correlation because of their depletion in the regolith samples. The regolith contains appreciable amount (4.0–6.0%) of K2O that shows largely increasing trend up-section. In the regolith samples, Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values are varying from 56.7 to 75.7 and 66.9 to 92.2, respectively. Both CIA and PIA of the regolith samples suggest moderate weathering intensity. The regolith samples show light rare earth elements (LREEs) enrichment in comparison to the parent rock because of their absorption by the clay minerals. The negative europium (Eu) anomaly might have been caused due to the weathering of plagioclases in them. The heavy rare earth elements (HREEs) show negligible variation in comparison to the parent rock despite moderate weathering under sub-humid climates in the regolith samples. The occurrence of K2O in the regolith obtained from the granite may increase nutrient value for agricultural purposes.