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Neotectonics of the Somogy hills (Part II): Evidence from seismic sections |
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| Authors: | L Csontos Magyari B Van Vliet-Lanoë and B Musitz |
| Institution: | aEötvös University, Department of Geology, Budapest, Pázmány s. 1/C, H-1117, Hungary bGeological Institute of Hungary, Budapest Stefánia u. 14. H-1143, Hungary cCNRS, Sédimentologie and Géodynamique, Université des Sciences et Techniques de Lille, 59655 Villeneuve d'Ascq cedex, France |
| Abstract: | The Somogy hills are located in the Pannonian Basin, south of Lake Balaton, Hungary, above several important tectonic zones. Analysis of industrial seismic lines shows that the pre-Late Miocene substratum is deformed by several thrust faults and a transpressive flower structure. Basement is composed of slices of various Palaeo-Mesozoic rocks, overlain by sometimes preserved Paleogene, thick Early Miocene deposits. Middle Miocene, partly overlying a post-thrusting unconformity, partly affected by the thrusts, is also present. Late Miocene thick basin-fill forms onlapping strata above a gentle paleo-topography, and it is also folded into broad anticlines and synclines. These folds are thought to be born of blind fault reactivation of older thrusts. Topography follows the reactivated fold pattern, especially in the central-western part of the study area. The map pattern of basement structures shows an eastern area, where NE–SW striking thrusts, folds and steep normal faults dominate, and a western one, where E–W striking thrusts and folds dominate. Folds in Late Neogene are also parallel to these directions. A NE–SW striking linear normal fault and associated N–S faults cut the highest reflectors. The NE–SW fault is probably a left-lateral master fault acting during–after Late Miocene. Gravity anomaly and Pleistocene surface uplift maps show a very good correlation to the mapped structures. All these observations suggest that the main Early Miocene shortening was renewed during the Middle and Late Miocene, and may still persist. Two types of deformational pattern may explain the structural and topographic features. A NW–SE shortening creates right-lateral slip along E–W faults, and overthrusts on NE–SW striking ones. Another, NNE–SSW shortening creates thrusting and uplift along E–W striking faults and transtensive left-lateral slip along NE–SW striking ones. Traces of both deformation patterns can be found in Quaternary exposures and they seem to be consistent with the present day stress orientations of the Pannonian Basin, too. The alternation of stress fields and multiple reactivation of the older fault sets is thought to be caused by the northwards translation and counter-clockwise rotation of Adria and the continental extrusion generated by this convergence. |
| Keywords: | Pannonian basin Transpressive deformation Neotectonics Adria–Europe interaction |
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