Using geodynamic modeling to test plate tectonic scenarios of the Mediterranean-Alpine area

Using geological and geophysical data, it is possible to reconstruct the past motion of tectonic plates involved in the Alpine orogeny and propose possible scenarios for their geological evolution. However, those scenarios have not yet been tested for geodynamic consistency.

Here, we perform 3D thermomechanical geodynamic simulations of the Mediterranean-Alpine area starting with a plate tectonic reconstruction at 20 Ma based on the work of Le Breton et al. (2017). The models include viscoelastoplastic rheologies and a free surface, and thus simulate the spontaneous occurrence of shear zones as well as the development of topography. Whereas some aspects of the tectonic reconstruction are well constrained (i.e. past position of the plates and subduction-collision fronts), many details such as the dip and length of the subducted plates, their thermal structure as well as their rheology, are unknown. The models are run forward in time to see to which extent they are consistent with the kinematic reconstructions. Perhaps unsurprisingly, our initial modelling attempts show a wide variety of behavior, including slab break off events and slab rollbacks in the wrong directions. Yet, in all cases tested so far, the model evolution does not reproduce the present-day geological setting, with Adria frequently moving too far towards the east and breaking apart internally, frequently no Alpine chain forming and in some cases new subduction zones developing within the Western Mediterranean that swallow Sardinia and Corsica.

Reproducing geological scenarios with thermomechanical geodynamic modelling thus requires substantial additional work, both from the modelling side (testing the effect of uncertain parameters on the behaviour of plates and subduction zones), as well as from the plate reconstruction side (assessing which parameters are well constrained and need to be reproduced).  Nevertheless, interesting insights can already be obtained from our models, and in our presentation, we will highlight some of the links between interacting subducting plates and plate motion.

Le Breton E, Handy MR, Molli G, Ustaszewski K (2017) Post-20 Ma Motion of the Adriatic Plate: New Constraints From Surrounding Orogens and Implications for Crust-Mantle Decoupling. Tectonics 36:3135–3154. doi: 10.1002/2016TC004443