9:45 AM - 10:00 AM
[AHW25-03] Contribution of deep-seated thermal water to groundwater in the lowermost part of Osaka Basin
Keywords:groundwater, depp-seated fluid
Relationships among hydrogen and oxygen isotope ratios and Cl- concentration of the studied waters suggested that the saline groundwaters in Miyakojima Formation were the mixture of seawater and meteoric water. The waters from basement rocks of mountain area were strongly diluted by meteoric water, while those beneath the plain were enriched in 18O with increasing Cl- concentration, a typical characteristic of Arima-type brine.
Relative chemical compositions of B-Li-Cl showed that the saline groundwaters in Miyakojima Formation were enriched in B, suggesting mixing of seawater and interlayer water dehydrated from clay minerals. While, many of those in the basement rock and Arima-type brines were enriched in B and Li, and such compositions were similar to those originated from volcanic and metamorphic fluids. The studied waters also had low lithium isotope ratio (δ7Li <+9‰), suggesting a high temperature interaction with rocks distributed along active faults; Arima-Takatsuki Tectonic Line, Uemachi Fault, and Uchihata and Kawachinagano Faults in the southern mountains. These groundwaters would include deep-seated water similar to the Arima-type brine.