Competing effects of post-rift thermal subsidence and contraction-induced tectonic uplift in inverted extensional basins: inferences from numerical models and observations from the Pannonian Basin

Basin inversion is usually associated with compressional uplift and erosion of the exhuming sedimentary succession, while the resulting uplift rates are governed by variable convergence rates and the inherited lithospheric structure. However, observations from the Pannonian Basin (Central Europe) record continuous basin-wide subsidence and deposition of anomalously thick sedimentary successions during its inversion. In this study, we investigate the controlling processes behind the subsidence and uplift patterns during the structural inversion of rifted basins.

We conducted a series of high resolution 3D numerical experiments to simulate the successive rifting and inversion stages of the Wilson cycle by applying the coupled I3ELVIS-FDSPM thermo-mechanical and surface processes numerical code. The code is based on staggered finite differences and marker-in-cell techniques to solve the mass, momentum and energy conservation equations for incompressible media, and it also takes into account simplified melting and surface processes.

The models show the successive stages of sedimentary basin formation during the extension. The variability of crustal and mantle thinning below the depocenters leads to spatial and temporal variations of subsidence rates during the syn-rift phase. At the onset of convergence, inversion localizes where the lithosphere is the hottest and thus the weakest. High convergence rate (i.e. 2 cm/yr) leads to localized uplift of the basin center above the asthenospheric upwelling, which also results in the flexural subsidence of the basin margins. This evolution ultimately leads to intraplate orogen formation and overprinting the former basin structure. In contrast, low convergence rate (i.e. 2 mm/yr) results in continuous thermal subsidence. Superimposed on this large-wavelength motion, localized contractional structures are formed. In this case, partial reactivation of the inherited extensional crustal fault zones is more dominant, while inversional structures are visible along the basin margins.

The modeling results are compared to the thermal and subsidence evolution of the Pannonian Basin during its Middle to Late Miocene rifting and Late Miocene to recent inversion.