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.

Interaction of mantle dynamics, crustal tectonics, and surface processes in the topography of the Romanian Carpathians: A geomorphological approach

“…Since 9 Ma, only fluvial sediments and volcanic products are preserved in the Transylvanian basin, which is affected by uplift and erosion from Pliocene to Quaternary . Moreover, although the heat flow in the basin is rather low (Demetrescu et al, 2001;Andreescu et al, 2002;Lenkey et al, 2002), the low velocity anomaly evidenced by tomography below the Transylvanian basin (Wortel and Spakman, 2000;Sperner and the CRC 461 Team, 2005;Martin et al, 2006;Ismail-Zadeh et al, 2008) and the time/space evolution of magmatism along the E-SE border of the basin suggest the upwelling of asthenospheric mantle (Chalot-Prat and Gîrbacea, 2000;Harangi and Lenkey, 2007;Seghedi et al, 2011). In this respect, the comparison of Fig.…”

Miocene facies associations and sedimentary evolution of the Southern Transylvanian Basin (Romania): Implications for hydrocarbon exploration

“…The basin has a low heat flow, in average 45 mW/m 2 , and ranges from 26 mW/m 2 in the basin center to 50-60 mW/m 2 to its margins (Demetrescu et al, 1992;Andreescu et al, 2002). The low heat flow fits well with the presence of a 100 km thick and unextended lithosphere and the Moho depth at 34 km (Tilit x a et al, 2006).…”

From nappe stacking to out‐of‐sequence postcollisional deformations: Cretaceous to Quaternary exhumation history of the SE Carpathians assessed by low‐temperature thermochronology

“…The paleogeothermal gradient is based on the present-day geothermal gradients obtained from the present-day surface heat flow, which is ∼40-60 mW/m 2 for the analyzed transect [Veliciu and Visarion, 1984;Demetrescu et al, 2001;Andreescu et al, 2002;Demetrescu et al, 2007]. Including thermal conductivities of 1.7-4.5 W/m/°C for the sampled rocks, a paleo-geothermal gradient of 20 ± 5°C/km was calculated for the entire transect.…”