Stable isotopes (δ13CDIC, δD, δ18O) and geochemical characteristics of geothermal springs of Ladakh and Himachal (India): Evidence for CO2 discharge in northwest Himalaya

Abstract

Geothermal fields are common in the north-western part of the Himalaya encompassing Himachal Pradesh and Ladakh region, owing probably to their link to the northward migration of the Indian plate and due to under plating. Twenty geothermal springs along the Indus and Nubra valleys of Ladakh region, Sutlej, Beas, and Parbati valleys of Himachal region have been studied. The major & trace element characteristics and stable isotopic composition (δ13CDIC, δ18 O & δD) of these springs were employed to trace their origin and process of metamorphic CO2 degassing. Surface temperature of these springs varies from 21 to 95°C, with an average of 56°C, whereas pH ranges from slightly acidic to alkaline 6.2–8.9 with an average of 7. Hydro-chemically these springs fall under the categories of HCO3: Cl: SO4 and Na+K: Mg: Ca types. Abundance of trace element in these spring waters, such as Fe, B, Li, Sr, Mn, Al, Mo, Zn, and As, were found in considerable amount, possibly due to the rock-water interaction. Springs of the study area contain high ratios of dissolved inorganic carbon (DIC) with concentrations of HCO3− ranging from 1300 to 13400, (average of 5297) μE. The δ13CDIC ratios of these springs vary from −8.4‰ to +1.7‰VPDB, which points towards the deeper source of their origin. δ18O composition of these springs range from −16 to −7.3‰vsmow with corresponding variation in δD varies from −123.5 to − 44.8‰vsmow indicating mixing of thermal water with a meteoric dominated reservoir as most of these samples fall on the line defined by Global Meteoric Water Line (GMWL). In the present study we have estimated the metamorphic CO2 flux using concentration of HCO3≈DIC of these springs and have found that the geothermal springs of the northwest Himalaya have potential to degas ∼2.9×107mol CO2 per year in the atmosphere. Further reservoir temperatures for these springs were also estimated applying standard dissolved silica geothermometers which varies from 42 to 107°C indicating their application in space heating and to generate electricity in certain cases.