Geochemistry of Fluid Inclusions in Travertines From Western and Northern Turkey: Inferences on the Role of Active Faults in Fluids Circulation

The understanding of the relationship between the geochemistry of fluids circulating during travertine deposition and the presence of active faults is crucial for evaluating the seismogenetic potential of an area. Here we investigate travertines from Pamukkale and Reşadiye (Turkey), sited in seismic regions and next to thermal springs. These travertines formed ~24,500–50,000 (Pamukkale) and ~240–14,600 years (Reşadiye) BP. We characterize fluid inclusions (FIs) and studied concentration of H2O, CO2, O2 + N2, and 3He, 4He, 20Ne, and 40Ar, and bulk composition (trace elements and δ13C-δ18O). FIs from both localities are mainly primary with low salinity and homogenization temperature around 136–140 °C. H2O is the major component followed by CO2, with the highest gas content measured in Pamukkale travertines. Concentrations of Ne-Ar together with O2 + N2 indicate that travertines from both areas precipitated from atmosphere-derived fluids. The 3He/4He is 0.5–1.3 Ra in Pamukkale and 0.9–4.4 Ra in Reşadiye. Samples with R/Ra > 1 are modified by cosmogenic 3He addition during exposure to cosmic rays. Excluding these data, FIs of Reşadiye are mostly atmosphere-derived. This implies a shallow formation where the circulation was dominated by meteoric waters, which is consistent with their young age. Instead, FIs of Pamukkale show mixing of mantle-, crustal-, and atmosphere-derived He, indicating that these travertines formed in lithospheric fractures. Based on the δ13CCO2 and δ18O of bulk rocks, we infer that travertines formed involving crustal- (mechanochemical rather than organic) and mantle-derived CO2. Trace elements of Pamukkale and Reşadiye show comparable rare earth element patterns. We conclude that travertines formed in response of seismogenetic activity.