Major elemental chemistry of geothermal springs from the Deccan traps: Solute sources and chemical fluxes

Abstract

Hot springs are largely originated through subsurface processes where surface water goes deep into the earth and get heated up by geothermal heat. These processes often occur in the areas of tectonic and volcanic activity. These spring waters, owing to their relatively higher temperature than surface water, have a higher solubility and hence, are characterized with higher solutes concentrations. This is an important solute source for the adjacent watersheds and are also capable of releasing substantial amounts of CO2 to the atmosphere. Despite of its large significance, very few attempts are made to understand this process, particularly from Deccan traps, in India. In this study, major ion chemistry of the hot springs from the Deccan trap regions was investigated to ascertain solute source and also, to quantify the CO2 release rate. In the Deccan region, hot springs are present along a linear belt along the west coast geothermal province, and they are supplying solute fluxes into the adjacent rivers of the western ghat. To achieve this goal, a field trip was carried out to the Deccan region for the collection of hot springs samples and river and groundwater during October 2023. All the geochemical analysis of the samples were carried at IISER Pune. The average dissolved silica and HCO3 of the hot spring samples are 1047 ± 307 μM and 848 ± 1222 μM respectively. Most of the hot spring samples are indicating Na-Cl rich water which might indicate seawater mixing acting as a dominant solute supplier. Solute flux from the river is much higher than the hot spring mainly because of higher discharge of the river and the dilution effect. The average reservoir temperature for these geothermal springs is estimated to be 111 ± 14 °C by silica geothermometer and 128 ± 58 °C by Na/K geothermometer. The CO2 release rate for the hot springs is computed by adopting a direct approach (Evans et al., 2008 and Tiwari et al., 2016) and found to be 4.6 × 105 moles/yr in total which is 3.8 × 104 times lower than that of the Himalayan hot springs. About half of the CO2 consumption in the Deccan region is counter balanced through CO2 release rate of the adjacent hot spring. Moreover, this study highlights the implications of Deccan hot springs in the context of solute supply and carbon cycle.