Geothermics of the Pannonian basin A talk in the frame of the Tibor Mendöl Workshop Lecturer: László Lenkey

Fundamentals of geothermics Geothermal gradient = grad T =  T ~  T z = dT/dz ~ ΔT/Δz Heatflow density (heat flow), q=-  T ~ q z = - dT/dz~ - ΔT/Δz, where is the thermal conductivity of rocks Heat transport equation:

Thermal lithosphere Herein et al., 2008 Ra=10e6Ra=10e7 2D spherical shell models of thermal convection in the mantle

Thermal lithosphere Herein et al., 2008

Thermal lithosphere Geotherms in the mantle Schubert et al., 2001

Definition of the lithosphere Lithosphere= (Thermal Boundary Layer, TBL)

Thickness of the lithosphere in Europe from Artemieva et al. 2006

Thickness of the lithosphere in Europe from Artemieva et al. 2006

Heatflow in Europe Pollack et al. 1993Artemieva 2003 Thickness of the thermal lithosphere

Geothermal conditions in Hungary Geothermal Database of Hungary (Dövényi, 1994)  4477 wells  deeper than 200 m  temperature higher then 30°C  all wells before temperature measurements Automatic correction of temperatures Lithology of the well Thermal conductivity data and trends

Geothermal database

Interpolation, heatflow Temperature corrections –Bottom hole temperature –Wells test –Outflowing water T Calculation of heatflow (condition: constant heatflow) Interpolation of T temperature [°C] depth [m] Thermal conductivity [W/mK] MAKO -2 Measured T Corrected temperature Thermal conductivity Interpolated temperature lithology For 1 layer:

Number of temperature measurements in wells EOV X EOV Y vagy több

(Horváth et al. 2005: Geodynamic atlas of the Pannonian basin) Heat flow in the Pannonian basin and surrounding areas

Processes influencing heatflow –Volcanic activity (e.g. Hargita) –Groundwater flow (e.g. Transdanubian Central Range) –Sedimentation/erosion (e.g. Makó trough) –Variation of thermal conductivity in 2D/3D (topography of the basement of the sediments e.g. Makó trough, Transylvanian basin) –Tectonics

Power of thermal springs at the feet of the Transdanubian Central Range

(Horváth et al. 2005: A Pannon-medence geodinamikai atlasza) Heat flow in the Pannonian basin and surrounding areas

Groundwater, helium and heat transport modell along a section in the Great Hungarian Plain Cserepes and Lenkey, 1999

Thickness of Neogene and Quarternary sediments

Sedimentation - model A thick and cold sediment layer is deposited at the surface Parameters of the model: –Thickness of the layer –Time of sedimentation –Time passed since deposition Z T T T0T0 T0T0

Infill of the Pannonian basin

Heatflow deficit due to sedimentation

Heatflow corrected for sedimentation

Transylvanian basin: variation of heat flow due to variation of the thermal conductivity of rocks

Thermal model of lithospheric extension

(Horváth et al. 2005: Geodynamic atlas of the Pannonian basin Thickness of the lithosphere in the Pannonian basin

Subsidence history Subsidence history off shore eastern cost of North America

Subsidence history

Summary Heat flow is an important geodynamic parameter Large scale variation in heat flow are caused by tectonic processes Small scale variations are due to groundwater flow, volcanism, variations in thermal condcutivity and heat production High heat flow in the Pannonian basin is a result of lithospheric extension occurred Ma The extension of the lithosphere was not uniform: the mantle part was more thinned than the crust