Gravity And Seismic Modeling In The Carpathian-Pannonian Region

An overview of the results based on a combined interpretation of the potential field and seismic data in the 2D and 3D space in the Carpathian-Pannonian Region is presented here. The interpretation of the gravity anomalies is based on the unified and homogenized gravity database from different countries. An integrated 2D modeling of the surface heat flow, geoid, gravity, and topography data simultaneously was applied with the aim to determine the lithospheric thermal structure along nine transects crossing the Western and Eastern Carpathians, Pannonian Basin and European Platform. The results indicate pronounced differences in the lithospheric thickness across the chain, as well as along strike of the Carpathian arc. Furthermore, the first 3D density model of the Western Carpathian-Pannonian Region was constructed based on the results of the newest seismic experiments. The temperature and density distribution in the uppermost mantle was calculated using a combination of petrological, mineralogical and geophysical information. This calculation was performed in order to enhance the 3D gravity modeling, particularly in the Pannonian Basin. The Pannonian Basin is characterized by an asthenospheric upwelling and thus by anomalous temperatures and densities in the uppermost mantle. The 3D model enabled also to perform gravity stripping that was applied as an additional analysis of the gravity field. It allows to identify the sources of the anomalies, to separate their effects and localize the lithospheric inhomogeneities. The gravity stripped image of the region revealed significant differences of the nature of the microplates ALCAPA and Tisza-Dacia from the surrounding regions. Due to the different methodologies and data used for the modeling, the results from the 2D and 3D modeling are slightly different. This is particularly true concerning the resulting densities and depth to the major boundaries, such as Moho and lithosphere-asthenosphere, mainly in the Pannonian region. Nevertheless, the results arc compatible and their main features are in agreement. In both models, a thick lithosphere (up to 130-150 km) is modeled underneath the Western Carpathians. Based on the 2D integrated modeling, the lithosphere reaches thickness of up to 240 km underneath the foreland of the Eastern Carpathians. Such lithospheric root is interpreted as a remnant of a subducted slab of the European plate. This is in contrast to the Western Carpathians, where no lithospheric root is observed/modeled. The lithospheric thickness varies from similar to 160 km underneath the Eastern Alps, to 90-140 km below the Bohemian Massif, 115-160 km beneath the Polish platform and 180-200 km under the East European Craton. The lithosphere is very thin in the Pannonian Basin, where it reaches thickness of 60-100 km. The recent results of modeling of refracted and reflected waves with use 2D ray tracing technique for profiles CEL01, CEL04, CEL05, CEL06 and CEL11 are shown in the last part of the chapter. Obtained P-wave velocity models of the crust and uppermost mantle are very complex and show differentiation of the seismic structure.The seismic models: (a) improved the knowledge on the crustal thickness and the crustal structure, which reflects the Alpine consolidation within the microplate ALCAPA and its junction with the European platform; (b) solved the problem of the definition of horizontal and vertical crustal boundaries and inhomogeneities (crustal composition) in the different tectonic units; (c) estimated the deep-seated tectonic contact between the Western Carpathians an ALCAPA on the one side and the European platform on the other hand; (d) terminated the amount of the Tertiary accretionary prism of the Outer Western Carpathians and its position compared to the platform; (e) distinguished of the physical differences of the crustal structure of the different tectonic units; and (f) helped to draft the geodynamic block model of the Carpathian-Pannonian Region. The depth of the Moho discontinuity in the studied region is changing from about 25 to about 45 km. Beneath some profiles, reflectors in the lithospheric mantle were found 10-20 km below the Moho, following its shape and generally dipping to the north. Interpretation of seismic profiles was the background for the tectonic description of two colliding lithospheric plates. The northern one is represented by older European tectonic units consists of the EEC and TESZ. The southern one - overthrusting - is built up by younger tectonic units of the Western Carpathians and the back-arc Pannonian Basin System (generating the microplates ALCAPA and Tisza-Dacia). It is suggested that present day complex structure is a result of the complicated continental collision between microplates ALCAPA and Tisza-Dacia and the south margin of the European Platform, which was accompanied by thermal back-arc extension beneath the Pannonian Basin System.