Dynamics of subduction systems with opposite polarity in adjacent segments: application to the Westernmost Mediterranean

Abstract

The objective of this thesis is to study the first-order dynamics of subduction systems characterized by opposite dip polarity in adjacent plate segments. The thesis consists of three different parts combining analog experiments and numerical models of very simple double subduction systems and its application to the Westernmost Mediterranean where a subduction system with opposite polarity in adjacent plate segments (double polarity subduction) has been proposed to explain the formation and evolution of this region. Part 1. Analog experiments of subduction systems with opposite polarity in adjacent segments

Firstly, we have studied the first-order plate dynamics of subduction systems with opposite polarity in adjacent plate segments by means of analog experiments. Laboratory experiments have been carried out in the Laboratory of Experimental Tectonics in Roma Tre University. Part 2. Reproducing analog experiments of subduction systems with numerical modeling

Some of the previous laboratory experiments have been performed by means of numerical modeling to compare and complement previous results and quantify the relevant physical parameters characterizing a double polarity subduction system. Around thirty-five numerical models, in addition to preliminary tests, have been performed although only fifteen are presented in this thesis showing the most outstanding and satisfactory results. The set of the numerical models have been run in the supercomputer MARENOSTRUM 4 (Barcelona Supercomputing Center, Spain) and BRUTUS (Swiss Federal Institute of Technology,Switzerland). Part 3. The Alboran and Algerian basins (Westernmost Mediterranean). A case study of double subduction with opposite polarity in adjacent segments.

Finally, a 3D numerical model of double subduction with opposite polarity in adjacent plate segments has been performed simulating the tectonic setting of the Westernmost Mediterranean. The evolution of the Alboran-Tethys slab (Betic-Rif slab) is reproduced in this tectonic scenario studying the influence of the adjacent plate segment. Around forty numerical models have been performed varying physical and geometrical parameters, including preliminary numerical tests. In this thesis only the final double polarity subduction model and a single plate subduction model are presented.

Results show that the progressive curvature of the Alboran-Tethys slab is due to the lack of a transform zone in its connection with the Atlantic oceanic to the west and the strong segmentation of the African margin. This produces larger retreat velocities in the eastern side of the slab, where a transform zone separates the Alboran segment from the Algerian segment, than in the western side. Trench retreat velocities of both plate segments are measured concluding that the opening of the Alboran Basin occurs around 22 Ma. The influence of the adjacent Algerian segment generates an asymmetrical flow pattern around both trenches slowing down the overall subduction process of the Alboran plate segment.