Towards understanding the roll-back subduction of narrow oceanic domains: inferences from the modelling of Carpathians subduction zone

Numerous subduction systems in the Meditteranean realm are derived from the subduction of narrow oceanic domains, which are too narrow to generate the means of a fully coupled two-dimensional thermo-mechanical numerical model that takes into account the visco-elasto-plastic properties of different lithospheric domains. The results show that the narrow extent of the Ceahlau-Severin Ocean commonly assumed by paleogeographic reconstruction cannot generate roll-back upon subduction, in particular for models that must assume that slabs do not penetrate the 660 km discontinuity. Therefore, we propose that the subduction of the Carpathians system must have an inherited component from a previous orogenic evolution, which will ensure sufficient slab-pull to generate roll-back in the Carpathians realm. The model is constrained by recent results in terms of mantle structure and geodynamic reconstructions, while multiple compositional, thermal distribution and geometrical scenarios are tested in successive models. In all of our models, roll-back is achieved, which indicates that the proposed inherited component can sufficiently explain the roll-back subduction of the aforementioned narrow oceans. The subducting oceanic slab does not penetrate the 660 km discontinuity, this is in agreement with seismic tomographic results from various Mediterranean subduction zones. The exact onset and dynamics of the roll-back are mostly controlled by the thermic age of the ocean and the convergence kinematics of the continental slabs. An outlook on possible future improvements to the model, such as taking into account pre-existing rheological weakness zones in the lithosphere, is discussed and the opportunity of a seismo-thermo-mechanical modelling to investigate the seismic cycle in the Vrancea-zone is highlighted.