Geodynamical models of lithospheric deformation, rotation and extension of the Pannonian Basin of Central Europe

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. The northward push of the Adriatic Block initiated the eastward displacement and rotation of both the Alcapa and Tisza blocks. We have constructed geodynamical models of the rotation and extension of the two Pannonian blocks. We analyse this process in terms of the competing influences of a NE 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. Deformation of the blocks included substantial strike-slip movements, together with shortening and possible extension across the Mid-Hungarian Line, which now separates the two domains. We use an idealised thin viscous sheet model of the continental lithosphere in which deformation is described by a nonlinear viscous constitutive relationship. Our approach is based on the finite element method, and we consider several distinct models of initial geometry, boundary conditions, and constitutive parameters. Rotation and deformation vary across both blocks, with anticlockwise rotation occurring in the Alcapa plate, and clockwise rotation in the Tisza block. The opposite rotations of the two plates led to NW-SE convergence in the space between the two Intra-Carpathian terranes. Subsequently both domains underwent extension dominantly in the NE-SW direction. Extension and internal rotation can be represented using a thin sheet model in which deformation is driven by an east- or northeast-directed outward traction of order 1 to 3 MPa. Internal buoyancy forces produced by thick crust from a prior phase of Alpine-style convergence appear to be a necessary element in the force balance that drives the extension process.