Heat flow modelling in the Transylvanian basin: Implications for the evolution of the intra-Carpathians area

Abstract

The evolution of sedimentary basins and their thermal structure are the result of the coupling between shallow crustal and deep lithospheric - mantle processes. When sources of shallow crustal deformation are not detectable, then deep lithospheric processes have the role to reveal the origin of these events. A particular method of investigating these deep processes is to evaluate their lithospheric thermal imprint, in particular when anomalous thermal values are exhibited. One such example is the Transylvanian Basin situated at the interior of the highly bended Carpathians chain, which shows lower heat flow values when compared with average cratonic values and even lower when compared with the neighbouring Pannonian extensional basin. The basin architecture suggests that a deep lithospheric - asthenospheric mechanism is responsible for Middle – Late Miocene subsidence, coeval with phases of Carpathian collision. The interplay between upper crustal evolution and deep lithospheric mechanics is investigated by means of 2D lithospheric-scaled heat flow modelling, simulating the present-day thermal regime of the basin. The heat flow correction for transient effects shows the great importance of paleoclimate and sedimentation during the evolution of the basin, calculated values being ~20% higher when compared with measured heat flow. The modelling implies that the low values of heat flow are the result of a combination of thermal effects of Middle – Upper Miocene sedimentation and the presence of depleted rocks in the basin basement, with their thickness dependent on the amount of enrichment in felsic magmatism during their evolution in a supra-subduction zone. The observations infer a thinned lower part of the mantle during the Miocene evolution of the basin, but the lithosphere thermal time constant suggests such changes do not affect the thermal regime at present day. Larger effects in the SE part of the basin are likely driven by the recent asthenospheric uplift due to the Vrancea slab descent.