Isotopic identification of CO2 from a deep origin in thermomineral waters of southeastern Spain

The overexploitation of the Alto Guadalentı́n detrital aquifer has led to an unusually high gas content in the waters, which is released as the hydrostatic charge decreases. The predominant gas proved to be CO2. Isotopic studies show that δ18O values are in the range −8.8 to −6.5‰ SMOW, δD ranges between −45 and −40‰ SMOW, excess deuterium lies between +8.0 and +27.4, and δ13C values lie between −8.1 and −3.8‰ PDB. This reveals that there is an enrichment in 18O as well as mixing processes between meteoric and deep circulating waters. Tectonic and seismotectonic studies indicate crustal thinning in the studied region and numerous normal, reverse and strike-slip faults marked by positive thermal anomalies. There is also evidence of present day tectonic activity.