Geochemical Eccentricity of Ground Water Allied to Weathering of Basalts from the Deccan Volcanic Province, India: Insinuation on CO sub(2) 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 sub(3)> Cl + SO sub(4) reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO sub(4), and NO sub(3) are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg-HCO sub(3) type progressively evolves to Ca + Na-HCO sub(3) and Na-Ca-HCO sub(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 sub(3) and Ca + Mg vs HCO sub(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 sub(3) supported by improved correlation coefficients between Na + Ca vs HCO sub(3) and negative correlation of Ca vs HCO sub(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 < R and R sub(k)) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite) products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component range from 6.98 to 36.65 tons/km super(2)/yr, respectively. The values of the CO sub(2) consumption rates range between 0.18 x 10 super(6 )mol//km super(2)/yr (groundwater) and 0.9 x 10 super(6 )mol/km super(2)/yr (surface water), which indicates that the groundwater forms a considerable fraction of CO sub(2) consumption, an inference, that is, not taken into contemplation in most of the studies.