A „Kapos-vonal” középső szakaszának szerkezeti-mélyföldtani viszonyai és neotektonikai jellegei a legújabb geofizikai vizsgálatok tükrében

The present study summarizes the results of the most recent geophysical research on the middle portion of the Kaposline (central Hungary). This work is dedicated to the memory of our unforgottable Colleague, Friend and Master, late Prof. Dr. Ferenc Horvath.As a first step a complex geophysical-geological database was formed integrating all available previous and newly measured 2D/3D reflection seismic, as well as borehole data, including also the results of new stratigraphic wells. A new, geologically and geometrically consistent 3D geological model of the study area was built by the interpretation of this integrated database. This 3D model consists of five geological horizons of basic importance within the study area (top pre-Cenozoic basement, top clastic/volcanic Lower Miocene, top marine Middle Miocene, top Endrőd and top Algyő Formations), as well as the interpreted faults. Considering the obtained new results, the previously published geologicalstructural models were critically re-evaluated and — if necessary — modified.One of the most important geological results of the research is the reambulation of the spatial extent, structural and facies relationships of the crystalline and Mesozoic basement rocks in the study area based on integrated evaluation of seismic and well data. Furthermore, the demonstration of the pronounced Early Miocene rifting event associated with the formations of several smaller basins with a depth up to 2 kilometers also represents a fundamental result. These basins were filled by a large amount of continental clastic sediments and coeval calc-alkaline volcanics. These findings underline the importance of the previously less known (and emphasized) role of the Early Miocene phase during the formation of the Pannonian basin.Based on the results of fault mapping the most important fault zones of the study area involve the ENE–WSW striking „Kapos line”, furthermore the NE–SW striking Dunaszentgyorgy–Harta, and the Bonyhad fault zones, the latter mapped first during this research. All of these fault zones are characterized by steep dip (≥60–70°). The Bonyhad fault zone in the southwest joins to northern imbricate zone of the Mecsek Mts. The general fault pattern of the study area is characterised mostly by NE–SW striking faults being (sub)parallel to the mentioned major fault zones. Structurally less important, NW–SE striking faults occur mostly south of the „Kapos line”.The results of detailed fault mapping clarified that a single, along strike structurally and geometrically uniform „Kapos line” does not exist in the study area. Instead, this fault zone can be divided into a western („Kapos-W”) and an eastern segment („Kapos-E”), which differ both in dip direction and — in accordance with previous literature dataobserved neotectonic activity. The eastern „Kapos line”, the Dunaszentgyorgy–Harta and the Bonyhad fault zones all show pronounced neotectonic activity. Moreover, they form the most important elements of a regional-scale, broad, neotectonic sinistral strike-slip shear zone consisting of predominantly NE–SW and ENE–WSW striking individual faults. The strike-slip kinematics of this shear zone is clearly indicated by the observed internal „flower structure” of the individual fault zones, as well as by the associated secondary fault pattern (Riedel faults).The location of the high-resolution 2D and pseudo-3D shallow geophysical surveys were determined based on the results of the introduced 3D geological-structural model of the study area. The results of these high-resolution geophysical surveys and the subsequent trenching and shallow boreholes clearly proved the Quaternary activity of the Dunaszentgyorgy–Harta fault zone. Moreover, the trenching indicated the Late Quaternary activity of this fault zone, since the tectonic deformation of the exposed Upper Pleistocene blown sand was observed and documented in the trench.Quaternary tectonic activity was also supported by numerous other previous and the present research-related observations, although they are not discussed in details in this study. The introduced results are also in accordance with literature data published on the tectonics of the eastern „Kapos-line” (Danube-Tisza interfluve and east of the river Tisza).The results presented in this study are related to the geological research program (FKP) of the Paks II project executed during 2015–2016.