Fluidumok, áramlási rendszerek és ásványtani lenyomataik összefüggései a budai-termálkarszton

The fluid evolution of the Buda Thermal Karst (BTK) has been ongoing since the Late Miocene. At that time the system was fully confined and only the thermal buoyancy influenced the flow of fluids in the system. Parallel with the uplift of the Buda Hills, the infiltration of fresh water into the system began; thus the subsequent evolution of the topography-driven groundwater flow brought about the superposition of the two fluid flow systems. This occurred with different prevailing driving forces: namely, the topography in the upper part and buoyancy in the lower. The uplift of the Gödöllő Hills also had an influence on the processes of the BTK and resulted in the evolution of fluid flow heading from the eastern, confined part of the system towards the River Danube. Consequently, the dominantly basinal fluids of the confining strata infiltrated into the underlying carbonate aquifers filled with meteoric water via vertical leakage. These changes were followed in the mineral paragenesis of the BTK. The western region of the BTK is part of the NE Trans-danubian Range and nowadays the carbonate aquifers are semi- or unconfined. The springs of this area represent the terminal points of local, intermediate and regional flow systems and they display the rock-water interaction along the flow path. The evaluation of the flow pattern could reveal the West–East direction of flow under the River Danube and the upwelling of fluids towards the discharge areas along the River Danube in the upper, shallow part of the system. The NaCl-type basinal fluids originated from the eastern-confining layers and they contribute to the regional flow component. West–Southwest of the River Danube, Mg²⁺- and SO₄₂ - rich water can be found. The results represent the hydraulically continuous flow sytem of the BTK, the asymmetric flow pattern at the boundary of unconfined and confined carbonate aquifers and, moreover, the significance of confining layers in the accumulation and dissipation of heat. The pressure conditions present in the system are nearly hydrostatic. The NE Marginal Fault also has a role in the differentiation of the discharge areas at the foothills of the Rózsadomb and the Gellért Hill. In the area behind the Gellért Hill an intermediate flow system appears; therefore, at the foothills of the Gellért Hill only thermal water is discharged. At the Rózsadomb the lukewarm and hydrothermal fluid discharge areas are close to each other. Thus the evidence strongly suggests that the respective hydrothermal components of the Central and Southern systems differ. The NaCl-type water of the eastern half of the basin contributes to the discharge of the regional flow path of the Central system. This system transfers H₂ S and CH₄ to the springs. In the case of the Southern System, the excess of sulphate in the water is more prevalent, and this may be in connection with the evaporite layers in the SW. On the basis of sulphur isotope analysis, the meteoric fluid component of the Rózsadomb receives its sulphur during infiltration through a pyrite-rich covering strata. The brief details mentioned here suggest that a better understanding of the fluid evolution of the BTK will contribute to the interpretation of hypogenic karstification and cave evolution in the area.