The Pannonian basin: Dynamic modelling of the transition from passive to active rifting

We examine a number of first order features of Pannonian basin evolution in terms of the feedback relation between passive far-field induced extension and active Raleigh-Taylor instable upwelling of the asthenosphere. We show that active mantle upwelling following a phase of passive extension are viable mechanisms explaining the Pannonian basin formation. The dynamic interplay between far-field driven passive extension and active thinning of the mantle lithosphere by convective upwelling beneath the rift zone is modelled using thermo-mechanical finite element methods. Our modelling results predict a first phase of passive lithospheric thinning which is followed by a second phase of late syn-rift to post-rift active mantle lithosphere thinning due to buoyancy induced flow beneath the rift zone. The pattern of coeval extension in the thinning region and compression in the flanking regions, predicted by the numerical model, may be explained by the buoyancy forces due to lithosphere thinning. It is demonstrated that time scales of and stresses generated by both processes are comparable. The model might also explain the occurrence of late shallow mantle related decompression melts in the Pannonian region and late regional doming.