Thermal budget of the Transylvanian lithosphere. Reasons for a low surface heat-flux anomaly in a Neogene intra-Carpathian basin

Abstract

SUMMARY This paper investigates the heat-flux budget of the Transylvanian Basin along a 240 km long WNW‐ESE geological profile. The thermal effects of sedimentation, erosion, crustal heat production and mantle heat flux on the thermal structure are studied. The thermal modelling is based on a 2-D finite-element model, which includes the effects of changing sedimentation rates, vertical and lateral variations in sediment thermal parameters, sediment compaction, as well as lateral variations in the crustal heat production and mantle heat flux. Even though the sedimentation history of the Transylvanian Basin began in Senonian time (90 Ma) and the total sediment thickness in the centre amounts to 8 km, half of the sediment cover was deposited in Neogene times from 16.2 to 5.6 Myr. The uplift and erosion of the basin began 5.6 Ma, resulting in a present-day average elevation of ∼600 m. The surface heat-flux pattern exhibits low values of ∼30 mW m −2 in the middle of the basin and higher values of ∼60 mW m −2 towards the margins. The low heat flux is explained by a combination of a depletion in crustal heat production, contributing with ∼15 mW m −2 , and a relatively low mantle heat flux. The present-day transient heat-flux depression caused by the rapid Neogene depositional history and the subsequent thermal relaxation (5.6‐0 Ma) amounts to ∼2.5 mW m −2 . Lateral variation of the heat flux at the base of the lithosphere cannot produce the surface heat-flux anomaly.