SUBSIDENCE ANALYSIS AND QUANTITATIVE BASIN MODELING IN THE STYRIAN BASIN (PANNONIAN BASIN SYSTEM, AUSTRIA)

We present the results of subsidence analysis and of quantitative basi n modelling using isostatical and flexural models for basin evolution along four cross-sections in the Styrian Basin, the westernmost subbas in 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 extensi on phase are below 1.04. The termination of subsidence during the Pann onian and a rapid Quaternary uplift phase can be explained by major ch anges in the regional stress field. A W-E cross-section through the no rthern Furstenfeld Subbasin provides a key for the understanding of th e dynamics of basin formation. It crosses a narrow Karpatian rift basi n, the metamorphic core complex of the Penninic Eisenberg Window and s hows an eastward tilting of the easternmost part of the basin during P annonian times. Uplift of the Penninic window can only be modelled wit h an extremely weak lithosphere (equivalent elastic thickness (EET) < 2 km), whereas a best fit between observed and modelled tilting is obt ained with an EET value of 5 km. These results suggest that the lithos phere was extremely weak during the onset of basin evolution in Ottnan gian-Karpatian times, probably caused by high extension rates and high heat flows associated with Karpatian to early Badenian magmatic activ ity. Subsequent cooling led to a pronounced increase in flexural rigid ity. An EET of 5 km fits well with estimations in other parts of the P annonian realm. Depth-dependent rheology models based on palaeo-heat f low estimates indicate a similar increase in lithospheric strength wit h time. The impact of Plio-Pleistocene volcanism on rheology appears t o be relatively modest, which can be explained by a deep position of t he magma chamber for this event.