2015 SPA - Mireia Peral - Dynamics of double-polarity subduction: application to the Western Mediterranean

[This post is participating at the 2015 Student Presentation Awards at ICTJA]

Plate tectonics describes large-scale Earth’s lithosphere motions through a number of thin rigid lithospheric fragments (plates) that are in motion relative to each other. The relative velocities of the plates are around 5 cm/year and most earthquakes, volcanic eruptions and orogenic belts occur in regions where different plates are in contact (plate boundaries). This study focuses on convergent margins, in particular on subduction zones, that place where two plates collide and one (commonly known as slab) moves under the other sinking into the mantle.

Figure 1. Scenario of the Western Mediterranean

 evolution (figure from  Chertova et al., 2014).

 Blue triangles indicate  the direction of 

subduction and the yellow arrows indicate the 

movemet of the plates.

The motivation of this work lies on the recent geodynamic model proposed by Vergés and Fernàndez (2012) to explain the evolution of the Western Mediterranean since 85 Ma. This model is based on the interaction of two plates which are characterized by opposite direction of subduction (double-polarity subduction). Our objective is to analyze the dynamic feasibility of this process and its consequences through a 3D numerical model.

The dynamic evolution of the Earth at large temporal and spatial scales, as subduction processes, is modeled as a flow problem and requires advance numerical techniques and high computation times. Numerical models of viscoelastic flow in 2D/3D have been developed to understand the dynamics of tectonic plates in large timeframes. The final model consists of two plates subducting into the upper mantle and the problem is driven by the density contrast between the lithosphere and the mantle beneath.

Our numerical results indicate that 2D and 3D single (one plate) subduction models with the same configuration result in similar slab morphologies. Anyway 3D models (because of taking into account the three dimensions) produce a faster subduction. In addition, a preliminary double subduction model, in which the two plates are separated 100 km one from the other, has been calculated. Comparing it with a single subduction model we observe slight differences in the subduction velocity and in the slab morphology near the contact area. We are currently checking the sensitivity of the double subduction models to modification of the space between the two plates and to different velocity boundary conditions. Moreover the lateral contact between the plates, the effect of temperature and geometries applicable to the Western Mediterranean region will be considered in future models. Finally, analogue models will be done in order to compare them with numerical solutions.

Figure 2. Time evolution of a 3D double polarity subduction model with a lateral separation of 100 km between plates.

This work is supervised by Manel Fernandez (ICTJA-CSIC) and Sergio Zlotnik (UPC, Barcelona) and is part of the project “Testing the geodynamic evolution of the Western Mediterranean (We-Me), financed by the CSIC as “Proyecto Intramural Especial” PIE-CSIC-201330E111.