Tectonic Setting of Sokolov Basin in Relation to Prediction of Thermal Water Discharge Zones
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GeoLines 20 GeoLines 20 44 45 2006 2006 and CELEBRATION 2000 Working Group, 2006. Lithosphe- ŚRODA P., CZUBA W., GRAD M., GUTERCH A., TOKAR- ric structure beneath trans-Carpathian transect from Precam- SKI A., JANIK T., RAUCH M., KELLER G.R., HEGE- brian platform to Pannonian basin – CELEBRATION 2000 DŰS E., VOZÁR J. and CELEBRATION 2000 Working seismic profile CEL05.J. Geophys. Res. (in print). Group, 2006. Crustal structure of the Western Carpathians KSIĄŻKIEWICZ M., 1977. Hypothesis of plate tectonics and the from CELEBRATION 2000 profiles CEL01 and CEL04: origin of the Carpathians. Ann. Soc. Géol. Pol., 47: 329-353 seismic models and geological implication. Geophys. J. Int. (in Polish, English summary). (in print). Tectonic Setting of Sokolov Basin in Relation to Prediction of Thermal Water Discharge Zones Radomír GRYGAR1, Arnošt GRMELA2, Jan JELÍNEK2, Jiří PÖPPERL3 and Roman GALEK3 1 Institute of geological engineering, VŠB – Technical University Ostrava, 17. listopadu, 70833 Ostrava, Czech Republic 2 Technical University Ostrava, 17. listopadu, 70833 Ostrava, Czech Republic 3 Sokolovská uhelná, a.s., Staré náměstí 69, 35600 Sokolov, Czech Republic The study area – the western part of the Eger Rift (the Sokolov be solved as emergency or warning states in relation to Karlovy basin) – belongs to the European Cainozoic Rift System (Kopec- Vary thermal springs. This problem may only be solved by con- ký 1978, Sengör 1995, Prodehl et al. 1995, Adamovič and Cou- ducting complex structural-tectonic analysis, based on parallel in- bal 1999, Dèzes et al. 2004). This system of graben structures terpretation of geophysical methods followed by regional hydro- and intraplate volcanic fields spreads over a distance of some geological prospecting. 1000 km, including the French Massif Central, the Upper Rhine The Sokolov Basin proper is a bilaterally tectonically limited, Graben, the Eifel, the North Hessian Depression, the Vogelsberg, transversally asymmetric depression, extending in WSW-ENE the Eger Rift and the Elbe Zone. Graben structures evolved on direction. In NW it is limited by the Krušné Hory Fault and also top of uplifted basement blocks (Variscan massifs); Tertiary and characterised by a system of minor parallel faults (especially the Quaternary volcanism is mainly concentrated on the flanks of Lipnice, Grasset, Sokolov and Nové Sedlo Faults), forming a sig- these graben structures along boundary faults or on the adjacent nificant tectonic zone of lithospheric range (Ziegler 1990). Ac- uplifted blocks. Dominantly (ultra-) alkaline, but also more evol- cording to Adamovič and Coubal (1999), most of this system’s ved, magmas were erupted. The main rifting phase with incipient accompanying faults are younger than the main stage of the Ohře graben formation and voluminous intraplate alkaline volcanism Rift volcanic and sedimentary development. lasted from about 42 Ma to 9 Ma. A detailed overview of the Another significant fault system of the Ohře Rift are the faults Cainozoic volcanic activity in the western part of the Bohemian running in NNW-SSE to NW-SE direction (in the Sokolov Basin Massif is given by Ulrych et al. (2003). The most recent expres- these are faults following the Svatava, Chodov and Karlovy Vary sions of magmatic activities within the European Cainozoic Rift faults). This system is especially intensively developed in the neigh- System are the CO2 degassing fields. The isotope (He, C, and N) bouring Cheb Basin, forming part of Mariánské Lázně tectonic composition of CO2-rich gas emanations of mineral springs and zone (e.g. Špičáková et al. 2000). The analysis of the Ohárecký Rift mofettes from the western Eger Rift (Weinlich et al. 1999, 2003) filling has shown that some of these faults had already been active gives evidence for the ascent of gases from fluid reservoirs in the synsedimentary. In the area of Sokolov basin the Chodov fault zone European subcontinental mantle. striking NW-SE belong to this tectonic system. It interfered with The Sokolov Basin is also a place of collision between long- SW limit (contact zone) of Variscan Karlovy Vary granite pluton term coal mining and spa Karlovy Vary protection. Both the and was reactivated later in post-rift stage. technology and the method of coal mining in Sokolov Basin are Emphasised in the most recent studies of the Ohře Rift tectono- strongly limited due to the existence of Karlovy Vary thermal sedimentary development has been the significance of W-E faults springs resources that have priority importance. Considering that that had already been active in the course of sedimentation as exten- from the structural and geological point of view, the geohydro- sion faults (Rajchl and Uličný 2000, Špičáková et al. 2000). dynamic systems of these resources form one single structure, ex- From the above it follows that the structural development tending as far as the Sokolov basin brown coal deposits, the pos- and the current tectonic architecture of the Sokolov Basin, simi- sibility of natural barrier layers being negatively impacted by hu- larly as to the entire Ohárecký Rift, have been affected by seve- man activity (i.e. mining technology in existing protection zones ral basic systems of normal faults, some of which show a less – especially in areas of hydrogeologically active faults and joint significant strike-slip component. Typical is above all the en-eche- systems) is extremely strong (Trčková et al. 2000). This has also lon arrangement of faults, horsetail-like virgation of faults, cur- become evident recently in the case of uncontrolled opening of vature in directional course, but also their normal fault listric ge- some old exit paths (old drills, old mining works, etc.) that had to ometry (se Fig. 1). Specific deformation conditions occur above GeoLines 20 GeoLines 20 44 45 2006 2006 plex approach was adopted. Both hydrogeochemical methods and methods of classic drill explorations, analyses of geological and tectonic data, analyses of diverse geophysical methods, and hydro- geological methods were applied. The clarification of hydrogeo- logical and hydraulic relations will help to more effectively protect the natural mineral resources of the spa town Karlovy Vary from potential impacts of brown coal mining. Acknowledgement This research is financially supported by the Grant Agency of the Czech Republic (research project No. 105/04/0521) Fig. 1. Low-angle listric normal fault with rollover fold strik- References ing W-E in the coal seam Antonín (Jiří Mine, Sokolov Basin). ADAMOVIČ L. and COUBAL M., 1999. Intrusive geometries and Cenozoic stress history of the northern part of the Bo- all in places of their mutual interference. To be expected in these hemian Massiť. Geolines, 9: 5-14. anomalous zones is the substitution of classic dislocation zones, DÈZES P., SCHMID S.M., ZIEGLER P.A., 2004. Evolution of accompanied by mylonitisation, by systems of brittle fracture, the European Cenozoic Rift System: interaction of the Al- above all by development of tensile joints. Thus, places of po- pine and Pyrenean orogens with their foreland lithosphere. tential outflow of underground or possibly thermal waters due to Tectonophysics, 389 (1–2): 1–33. joint secondary porosity have formed. KOPECKÝ L., 1978. Neoidic taphrogenic evolution and young In spite of safety measures aimed at stabilising the hydroge- alkaline volcanism of the Bohemian Massif. Sborník geo- ologic situation of gas-cut thermal springs of the Karvoly Vary logických věd, Geologie, 31: 91-107. type in the coal basin basement, situations arise in the Družba RAJCHL M. and ULIČNÝ D., 2000. Evolution of basin-fill and Jiří open-pit mines (Sokolov Basin) during mining which geometries in the Most Basin: implications for the tec- represent uncontrolled interference with the natural regime of tonosedimentary history of the Ohře Rift (Eger Graben), these groundwater bases. Especially dangerous are the old mine North Bohemia. Proceedings ofthe 5th Meeting ofthe Czech workings of abandoned deep mines. An example of such situa- Tectonic Studies Group, Geolines, 10: 62-63. tion is the inrush of thermal waters in the Jiří open-pit mine in SENGÖR A.M.C., 1995. Sedimentation and tectonics of fossil January 2003, occurring in the wall of abandoned working base, rifts. In: C.J. BUSBY and R.V. INGERSOLL (Editors), Tec- in close vicinity of the Grasset Fault. The inrush was monitored tonics of Sedimentary Basins, Blackwell Science, Oxford, as to its yield and hydrogeochemical composition, before the 53-117. place of inrush was sealed by inner dump. ŠPIČÁKOVÁ L., ULIČNÝ D. and KOUDELKOVÁ G., 2000. In spite of the relatively high resistance of thermal structu- Tectonosedimentary history of the Cheb Basin (NW Bohe- res to outside impacts, the disturbance of natural steady regime mia). Proceedings of the 5th Meeting of the Czech tectonic with resulting impact on Karlovy Vary thermal springs may not Studies Group, Geolines, 10: 69-70. be ruled out. In such event the restoration of conditions would TRČKOVÁ J., VYLITA T., PĚČEK J. and HANZLÍK J., 2000. be most difficult and lengthy, with far-reaching consequences Dopady těžby hnědého uhlí na zvodněný systém sokolovské for the spa town of Karlovy Vary. pánve v souvislosti s ochranou karlovarských pramenů. Acta From the viewpoint of geotechnical stability of the seam base- Montana IRSM AS CR (2000), series AB, 115: 187-206. ment, the most critical situation is in the vicinity of the Grasset ULRYCH J., PIVEC E., LANG M., BALOGH K. and KROPA- and Nové Sedlo faults in Jiří open pit mine (thermal waters unco- CEK V., 1999. Cenozoic intraplate volcanic rocks series of vered overpressure reaches up to 0.6 MPa). the Bohemian Massif: a review. Geolines, 9: 123-129. When studying the hydrogeologic relations between the ground- ZIEGLER P.A., 1990. Collision related intraplate compression water basement of the Sokolov coal basin and the Karlovy Vary ter- deformations in western and central Europe. Journal of mal spring used for balneological purposes, a systematic and com- Geodynamics, 11: 357-388..