Mireia Peral defended her PhD Thesis entitled “Dynamics of subduction systems with opposite polarity in adjacent segments: application to the westernmost Mediterranean” on June On 3rd June. The main purpose of the work, which has been supervised by Manel Fernández, researcher at ICTJA-CSIC, and Sergio Zlotnikm from Universitat Politècnica de Catalunya (UPC), was to study and to better understand the evolution and dynamics of double subduction systems characterized by opposite dip polarity determining the relevant physical parameters that characterize a process that, according to Mireia Peral, is “still poorly understood”.

Peral analysed by means of analogue and numerical modelling the evolution of this type of subduction processes that stands out for their complexity. "In certain regions of the Earth great tectonic complexity is observed, such as in the Mediterranean region, where the presence of micro-plates generates subductions with different orientations and whose evolution are still poorly understood", pointed out Mireia Peral.

“A single subduction process is already complex but the process becomes more complicated if there are two plates subducting in opposite directions. This is mainly due to the interaction of the mantle flow induced by both plates. As a subduction plate pulls down the mantle material which behaves as a fluid at geological time scales. In the case of a double subduction system, fluxes are generated in the contact region between both slabs with opposite directions and affect the evolution of the process”, said Peral.

"To configure the different models that are part of the work, the real dimensions of nature, the physical properties of the rocks and the geological data of the study region have been taken into account”, said the thesis author. According to the results, in the double subduction systems the interaction of the mantle flow produces additional deformation in the plates and variations in the subduction velocities that are not observed in the single subduction systems.

The analogue models presented in the thesis were performed in the Laboratory of Experimental Tectonics of the University of Rome III (Italy). These models were set up with “different configurations to study the influence of the width of the plates and their initial lateral distance. These experiments allowed Peral to analyse the interaction between both plates, observing their deformation and deviation as well as the subduction velocities and the flow pattern of the mantle".

Highly computing demanding numerical models were calculated on the “Euler” supercomputers at the ETH in Zurich and “MareNostrum” at the Barcelona Supercomputing Center (BSC). Peral developed several numerical models based on the previous analogue experiments in order to quantify the relevant physical parameters that could not be measured in the laboratory, allowing at the same time to calibrate the different models developed by both methodologies.

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Furthermore, Mireia Peral designed a 3D numerical model to be applied to the Western Mediterranean region, concluding that the double subduction process with opposite polarity could explain the formation and evolution of this region, and estimating the opening of the Alboran Basin 22 million years ago in accordance with geological data.

"The study of this process in the Mediterranean region is interesting because there is still great controversy about the formation and evolution of this region”, explains Peral. The 3D model of the Westernmost Mediterranean zone presented in the thesis is, according to Peral, “a starting point to a more detailed study that includes, for example, more accurate geometries, the convergence of the Iberian and African plate and magmatic processes related with mantle flow”.

“This work sheds light to the dynamics of double subducting systems with opposite polarity and opens the door to study other zones like Western Tibet, Western Pacific or New Zealand where this type of subducting process is proposed”, said Peral.

“The results highlight the importance of studying a geodynamic process by means of different methodologies. Analogue and numerical experiments were consistent, but they showed some differences that suggest the need of doing a more detailed study from a methodological point of view”, said Peral.

The PhD thesis defense was planned for last 20th March, but it had to be postponed due to the coronavirus outbreak. Finally, Peral was allowed to make her dissertation online. Antoni Teixell, from the Univeristat Autónoma de Barcelona (UAB), Pilar Queralt, from Universitat de Barcelona (UB) and Sara Figueras, from Institut Cartográfic i Geològic de Catalunya (ICGC) were the members of the thesis tribunal. Peral received a “Cum Laude” distinction for her dissertation.

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