Geothermics of the Pannonian basin and its bearing on the neotectonics

Abstract

Different aspects of the geothermics of the Pannonian basin are investigated from the viewpoint of neotectonics. A heat flow map of the basin and the surrounding region is presented. It is shown that the high heat flow of the Pannonian basin, the subsidence and maturation history of the Neogene sediments can be explained in general by Middle Miocene extension and thinning of the lithosphere. To obtain fit to the observed vitrinite reflectance data in the peripheral areas uplift and erosion had to be assumed, which started in the Late Pliocene. For the same time period a thermo-mechanical extensional model would predict thermal subsidence, therefore, the observation of this late stage uplift suggests that the thermal subsidence has been overprinted by tectonic forces, like an increase of intraplate stress. Groundwater flow in porous sedimentary rocks or in fractured rocks disturbs the geothermal field making difficult the interpretation of the heat flow in terms of simple conductive models. However, from the viewpoint of tectonics the occurrence of thermal springs is helpful, because most of the thermal springs occur along faults. Almost half of the thermal springs in Hungary are found along faults, which have been active during the Late Pliocene through Quaternary period. The relationship between the geothermics and the seismicity of the Pannonian basin has also been investigated. It is shown that the seismicity can be understood in terms of collision of the Adriatic microplate with Europe and differences in thermal state of the lithosphere. The tectonically less active Bohemian Massif, Ukrainian and Moesian Platforms form a cold rigid frame of the Pannonian basin. The Pannonian basin and the Dinarides comprise a complex seismotectonic unit. The Pannonian basin, which is characterized by high heat flow, has low to moderate seismic activity, with earthquakes occurring in the upper crust. The Dinarides, which are characterized by low heat flow, have high seismic activity and the focal depth of the earthquakes reaches 40 km. Rheological profiles constructed for the region show that in the Pannonian basin only the upper 10–14 km thick Correspondence to: L. Lenkey (lenl@freemail.hu) part of the crust has brittle strength, as opposed to the Dinarides where the brittle part of the crust is 20–24 km thick, and there is a mechanically strong layer also in the upper mantle.