Geochemical Eccentricity of Ground Water Allied to Weathering of Basalts from the Deccan Volcanic Province, India: Insinuation on CO2 Consumption

Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline earth elements to total cations and HCO 3 >Cl + SO 4 reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO 4 , and NO 3 are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg–HCO 3 type progressively evolves to Ca + Na–HCO 3 and Na–Ca–HCO 3 class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO 3 and Ca + Mg vs HCO 3 supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation of CaCO 3 supported by improved correlation coefficients between Na + Ca vs HCO 3 and negative correlation of Ca vs HCO 3 , respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function of selective dissolution of olivine > pyroxene followed by plagioclase feldspar. The data suggest siallitization ( L