3D geophysical and thermal modelling of the northeast Carpathian lithosphere: Implications for geothermal potential of the Baia Mare region

The presented study is part of an international multidisciplinary project aiming to investigate the geothermal potential of the Baia Mare volcanic province in north-western Romania. We integrate existing geological, geochemical, hydrogeological, and geophysical data into a 3D lithospheric temperature model. In addition, new seismic reflection and broadband magnetotelluric data, acquired in the study region, provide additional constraints on the crustal-scale structures possibly controlling the transport of deep heat to the surface.

The study area is located within the Neogene Inner Carpathian volcanic arc and includes the area of the recent crustal uplift between the north-eastern part of the Pannonian Basin and the Transylvanian Basin. Borehole temperature measurements showed a geothermal gradient of 45-55 ^oC km^-1 and temperatures higher than 150 ^oC at depths of 3000 m, the highest values of heat flow recorded to date in Romania. The region is known for surface hot springs and hydrothermal and epithermal volcanic ore deposits.

The heterogeneous pre-Neogene basement contains metamorphic and igneous rocks deformed or emplaced during Precambrian to Paleozoic orogenic cycles and a Triassic-Paleogene sedimentary cover with a variable radioactive heat production rate. The Miocene magmatic plumbing system within the Neogene sedimentary sequence includes intrusive bodies of 1-10s of km size. Crustal hydraulic properties and associated hydrothermal systems are possibly controlled by the regional Bogdan Voda – Dragos Voda strike-slip faults system, which provided pathways for the Miocene volcanic emplacement and sub-volcanic intrusions.

The knowledge of deep lithospheric structure is important for the characterisation of sedimentary basins with a geothermal exploration potential. In this contribution, we present geophysical and geological data and describe the construction of a regional 3D lithospheric temperature model. The structural model includes sedimentary successions, crystalline crustal layers and lithosphere-asthenosphere boundary constrained by gravity, seismic tomography and magnetotelluric data. The temperature modelling is performed by solving 3-D steady state heat conduction equation using a finite element method. We compare the model responses with available surface heat flow and borehole temperature measurements and discuss the role of local crustal heterogeneities, transient heat transfer and fluid circulation on the thermal state of the Baia Mare region.