δ18 O and δD shifts in adjacent aquifers with different types of geothermal water

摘要

There are geothermal water samples from adjacent deep basin and uplifted basement areas in which the δD and δ18O values deviate from the LMWL. The reason for the deviation is mixing of paleo-meteoric water and the most mineralized NaHCO3-type water in the deeper basin areas. Above the uplifted basement,besides mixing of paleo-meteoric water with brackish water trapped in the sediments, a Rayleigh-type process is hypothesized, based on a non-linear correlation between Cl- and the isotope δ values. This process may be a consequence of the changing composition and chemical potential in the water phase of the water-rock system,due to the mixing. The NaHCO3-type end-member is probably the freshened water of Lake Pannon trapped during sedimentation at the very end of the Late Miocene. The brackish end-member originates from Middle Miocene seawater.