Crustal structure at the contact of the Dinarides and Pannonian basin based on 2-D seismic and gravity interpretation of the Alp07 profile in the ALP 2002 experiment

SUMMARY

The area of this study includes the contact between the Dinarides and the Pannonian basin, as a relation between the Adriatic microplate and Pannonian segment. Our analysis was carried out on profile Alp07, which is a part of the ALP 2002 experiment. ALP 2002 was large international seismic experiment that focused on the lithospheric structure of the Eastern Alps and surrounding areas. Profile Alp07 is one of several refraction and wide-angle reflection profiles located in the transition from the Adriatic microplate, through the Dinarides, and into the Pannonian basin. This 300-km-long profile extends from Istra, Croatia to the Drava River at Hungarian–Croatian border in a WSW–ENE direction. It is oriented approximately perpendicular to the Dinarides, the main faults in the Adriatic region, and the contact between the Dinarides and Pannonian basin. 2-D seismic modelling was done using tomographic inversion and ray tracing techniques. The Moho depth is the greatest in the area of the Dinarides, reaching about 40 km and is shallowest (30–20 km) in the Pannonian basin area. At the boundary between these provinces, the depth changes rather suddenly. In order to obtain additional constraints on the crustal structure, 2-D gravity modelling was also performed. The layer boundaries were retained from the seismic model as there was no need to change them during modelling, since varying densities in the model produced a good fit to the data. A geological model was constructed based on both geophysical models. Three types of the crust were found along profile: the Dinaridic and the Pannonian crusts that are separated by a relatively narrow transition zone. The Dinaridic upper crust is characterized by low seismic velocities and densities, but its lower crust has high velocities and densities. The Pannonian crust can be seen as unique layer characterized by both low seismic velocities and densities. Large lateral and vertical changes in densities and seismic velocities can be found in the transition zone. Troughs in the seismic model at the level of the Mohorovičić discontinuity are interpreted as major faults in the lithosphere. Three main lithospheric faults were identified: in northeastern part of the Dinarides under the Sava depression and under the Drava depression. The first one may be considered as a result of subduction of the Adriatic microplate under the Pannonian segment. Similar movements are also defined within the transition zone, where the Pannonian segment is gradually rising over on the Adriatic microplate.