Migration of basin formation and contrasting deformation style in the south-western Pannonian Basin (central Europe)

The Pannonian Basin is a continental extensional basin system with various depocentres within the Alpine–Carpathian–Dinaridic orogenic belt. Along the western basin margin, exhumation along the Rechnitz, Pohorje, Kozjak, and Baján detachments resulted in the cooling of variable units of the Alpine nappe stack. This process is constrained by thermochronological data between ~25–23 to ~15 Ma (Fodor et al., 2021). Rapid subsidence in supradetachment sub-basins indicates the onset of sedimentation in the late Early Miocene from ~19 or 17.2 Ma. In addition to extensional structures, strike-slip faults mostly accommodated differential extension; branches of the Mid-Hungarian Shear Zone (MHZ) could also play the role of transfer faults. During this period, the hanging wall margin of the detachment system, i.e., the pre-Miocene rocks of the Transdanubian Range (TR) experienced surface exposure, karstification, and terrestrial sedimentation. After ~14.5 Ma faulting, subsidence, and basin formation shifted north-eastward and reached the TR where fault-controlled basin subsidence lasted until ~8 Ma. 3D thermo-mechanical forward models analyze this depocenter migration and predict the subsidence and heat flow evolution that fits observational data. These models consider fast lithospheric thinning, mantle melting, lower crustal viscous flow, and upper crustal brittle deformation. Models suggest ~150–200 km of shift in depocenters during ~12 Myr. Simultaneously with depocenter migration, the southern part of the former rift system, near or within the MHZ, underwent ~N–S shortening; the early syn-rift basin fill was folded and their boundary faults were inverted. Deformation was dated to ~15–14 Ma („middle” Badenian) and continued locally to ~9.7 Ma while north of the MHZ the TR was still affected by modest extensional faulting. The particularity of this shortening is that it happened during the post-rift thermal cooling stage. The low-rate contraction and related uplift rarely exceeded this regional thermal subsidence. MOL Ltd. largely supported the research. The research is supported by the scientific grant NKFI OTKA 134873 and the Slovenian Research Agency (No. P1-0195). Fodor, L., Balázs, A., Csillag, G., Dunkl, I., Héja, G., Jelen, B., Kelemen, P., Kövér, Sz., Németh, A., Nyíri, D., Selmeczi, I., Trajanova, M., Vrabec, M., Vrabec, M. (2021): Crustal exhumation and depocenter migration from the Alpine orogenic margin towards the Pannonian extensional back-arc basin controlled by inheritence. Global and Planetary Change 201, 103475. 31p. https://doi.org/10.1016/j.gloplacha.2021.103475