Transylvanian heat flow in the presence of topography, paleoclimate and groundwater flow

Abstract

The Transylvanian Depression (TD) is located in the inner part of the Carpathian orogen and shows a marked heat flux low of 30 mW m −2 in the centre, increasing to 60 mW m −2 towards the margins. It is the purpose of the paper to asses the possibility that the observed heat flux in the TD is a consequence of disturbances of the shallow geothermal gradient caused by topography, topographically driven ground water flow and climatic changes. The thermal effects of topography, topographically driven groundwater flow and paleoclimate have been investigated using two-dimensional finite element models. The results show that topography can induce a decrease in heat flux at hill crests and an increase at the bottom of valleys. Topographically driven ground water flow accentuates the effect above ∼1000 m and decreases it below. For the characteristic amplitude and wavelength of topography in Transylvania the heat flux corrections for the cumulated effect of topography and water flow are maximum 1 mW m −2, which is insignificant. Paleoclimate potentially has a large thermal effect. Temperature variations associated with the last glaciation can produce a significantly increasing gradient with depth, which is present in the majority of measured wells. Inversion of six wells confirmed that the curvature in the temperature profiles is consistent with the climatic cooling of the last glaciation. The paleoclimatic effect may induce heat flow corrections in the range 3–7 mW m −2.