3-D numerical modeling of subduction evolution of the western Mediterranean region

This thesis is focused on various aspects of the evolution of the western Mediterranean region. Particularly, on modeling of the 3-D subduction evolution of the Rif-Gibraltar-Betic slab in the western Mediterranean region by means of 3D thermo-mechanical modeling and investigation its dependence on factors influencing the subduction dynamics. This region underwent a long and complicated history of slab rollback and lithosphere tearing, for which the only direct observations come from its geological history and present day mantle structure inferred by tomographic data. Different tectonic reconstructions were proposed for this region based on these observations. Despite the general agreement on the initiation of the subduction process around 35 Ma and slab buoyancy being a major driving force which forms the present day slab under Gibraltar these reconstructions propose distinctly different initial parameters of the subduction zone, as well as temporal evolution of the region during the last 35 My. To investigate the basic numerical and rheological settings, which allows for the development of a free rollback process this research had started with 2D numerical experiments of the evolution of the subduction process. This first phase also included investigation of influence of the side boundary conditions. The use of open side boundaries proved extremely important for reaching the overall goal of 3D numerical experiments. It was demonstrated that implementation of the open side boundary conditions allows to significantly reduce lateral domain size and computational time without any considerable impact on the flow pattern inside the modeling domain. A wide range of parameters for composite rheology was tested, which was later used for the 3D numerical modeling. In the second part of the thesis we extended the experiments to 3D numerical modeling domain to simulate the evolution of the subduction process in western Mediterranean since 35 Ma till present. Three distinctly different kinematic reconstruction scenarios were tested, which all claimed to reproduce the present day mantle structure as imaged by tomography studies. It was shown that these tectonic reconstructions after 35 My of subduction evolution led to completely different slab position and shape. As a result, different mantle structure was observed. For obtaining the most realistic model in terms of fitting present day mantle structure and timing of the evolution of the subduction process introduction of a second small subduction system to the east proved key and resulted in predicting the observed cold anomaly in this region interpreted as the Kabylides slab. The fit with two major temporal constraints: slab arrival to the African margin in Middle Miocene and slab stalling under the Gibraltar region since the Tortonian were significantly improved by including the Kabylides slab. On the basis of a successful model for the evolution of the western Mediterranean region, the research was continued with investigation of the influence of different absolute plate motion reference frames on the dynamics of the subduction process. On the basis of the relative Africa-Iberia convergence [van Hinsbergen et al., 2014] three different absolute plate motion reference frames were implemented and tested against prescribed absolute plate motions based on Doubrovine et al. [2012]. This demonstrates that for modeling of the evolution of complex real-earth subduction, on scales and style comparable to the western Mediterranean subduction, it is crucial to constrain numerical models by absolute plate motions. 1. Doubrovine, P. V., B. Steinberger, and T.H. Torsvik (2012), Absolute plate motions in a reference frame defined by moving hotspots in the Pacific, Atlantic and Indian oceans. Journal of Geophysical Research, 117, B09101, doi: 10.1029/2011JB009072. 2. van Hinsbergen, D.J.J., R.L.M. Vissers, and W. Spakman (2014), Origin and consequences of western Mediterranean subduction, rollback, and slab segmentation, Tectonics