14 May, 2009 (16:00 GMT), 5 Merrion Square, Dublin 2.

Speaker: Dr. Piroska Lorinczi.
Title: Geodynamical Models of the formation of the Carpathian-Pannonian Region of Central and Eastern Europe.

Abstract:

As part of the Alpine orogenic system the Pannonian basin formed by extension of the crust and lithosphere between about 17 and 12 million years ago. The two major crustal blocks of the Pannonian basin, Alcapa  (Alpine-Carpathian-Pannonian) and Tisza, underwent a complex process of rotation and extension of variable magnitude during the Tertiary.  Opposite rotations of the two plates led to NW-SE convergence and NE-SW extension in the space between the two Intra-Carpathian terranes. We have constructed geodynamical models of the rotation and extension of the two Pannonian blocks. We aim to show, using 2D numerical models, how the two blocks deformed under the influence of a NW push by the Adriatic block, a NE pull from a retreating subduction zone on the eastern Carpathians, and the internal buoyancy forces arising from crustal thickness variations. Present-day tectonic activity in this region is concentrated underneath the southeastern part of the Carpathians, the Vrancea region. Strong earthquakes occur at intermediate depths beneath Vrancea in a narrow, nearly vertical source volume between about 70 and 200 km depth. This phenomenon is often attributed to subduction of oceanic lithosphere. However an alternative explanation to this deep seismicity is that downwelling of the continental mantle lithosphere is produced by gravitational instability. Three dimensional finite deformation models of the gravitational instability of the continental lithosphere, based on the finite element method, demonstrate that the Rayleigh Taylor mechanism can explain the present distribution of deformation within the downwelling lithosphere, both in terms of distribution of seismicity and amplitude of strain rates.