Subsidence analysis and quantitative basin modelling in the Styrian Basin (Pannonian Basin System, Austria)

We present the results of subsidence analysis and of quantitative basin modelling using isostatical and flexural models for basin evolution along four cross-sections in the Styrian Basin, the westernmost subbasin of the Pannonian Basin System. Subsidence analysis reveals a first Ottnangian-Karpatian synrift phase. Our local isostatic models predict crustal stretching values up to 1.3 and subcrustal stretching values of 1.6 for this event. Stretching factors of a minor Sarmatian extension phase are below 1.04. The termination of subsidence during the Pannonian and a rapid Quaternary uplift phase can be explained by major changes in the regional stress field. A W-E cross-section through the northern Fürstenfeld Subbasin provides a key for the understanding of the dynamics of basin formation. It crosses a narrow Karpatian rift basin, the metamorphic core complex of the Penninic Eisenberg Window and shows an eastward tilting of the easternmost part of the basin during Pannonian times. Uplift of the Penninic window can only be modelled with an extremely weak lithosphere (equivalent elastic thickness (EET) < 2 km), whereas a best fit between observed and modelled tilting is obtained with an EET value of 5 km. These results suggest that the lithosphere was extremely weak during the onset of basin evolution in Ottnangian-Karpatian times, probably caused by high extension rates and high heat flows associated with Karpatian to early Badenian magmatic activity. Subsequent cooling led to a pronounced increase in flexural rigidity. An EET of 5 km fits well with estimations in other parts of the Pannonian realm. Depth-dependent rheology models based on palaeo-heat flow estimates indicate a similar increase in lithospheric strength with time. The impact of Plio-Pleistocene volcanism on rheology appears to be relatively modest, which can be explained by a deep position of the magma chamber for this event.