Mobilization and redistribution of elements during basalt weathering in the subtropical condition of Central India

Abstract:

Basalt is most weatherable rock with its importance in sequestering atmospheric CO_2. The Deccan basalts cover almost 15% of geographical area of India. Considering its significance, we studied the weathering of Deccan basalts in two different climatic zones viz., monsoon/humid subtropical (Pithampur) and dry tropical climate (Bherughat) in and around Indore, central part of India. Our objective here was to study the elemental behavior in different zones of basaltic weathering profile (viz. bedrock, saprolith, saprolite and soil) which has been studied using geochemical mass-balance approach. The elements (major, trace and REE) were analysed on XRF and ICP-MS and the geochemical data was used to calculate the chemical index of alteration (CIA) and geochemical mass balance values (Ʈ). CIA was calculated to know the degree of weathering whereas geochemical mass balance calculations were done to understand mobilization and redistribution of elements during the basalt weathering. The result indicates lower range of CIA from 57 to 77 for Bherughat as compared to Pithampur, where CIA ranges from 60 to 87. The mass balance values of the elements suggest that both the weathered profiles show low to moderate depletion of mobile elements, however, in Bherughat slight enrichment of K was observed suggesting less weathering of K-bearing primary minerals or K adsorption on clay minerals. Low to moderate degree of depletion of trace elements was also observed. However Sc and Ni in Pithampur and Cr and Ni in Bherughat profile show high enrichments. Low degree of depletion of REE was observed for Bherughat profile. Whereas, low enrichment was observed in saprolith zone of Pithampur profile. This understanding will be useful to understand implications of increasing CO₂ on carbon sequestration and nutrient cycling in the soils of basalt weathering profiles.