- Thesis title: Numerical modeling of continental collision and intraplate deformation. Application to the Cenozoic geodynamic evolution of North Iberia.
- Author: Ángel Valverde Pérez (GEO3BCN-CSIC)
- Date: 10 February 2021, 12:00 h
- Place: Online. .
This thesis aims at improving the current understanding of the geodynamic controls on tectonic deformation during plate collision, using the Cenozoic evolution of Iberia as a case scenario. Despite the vast efforts during the last decades, there is a limited understanding today about what plate properties control the propagation of tectonic deformation towards the interior of tectonic plates. Meanwhile, the classic enigmas about the timing and the processes involved in the construction of the Iberian topography also persist: What is the origin of the high average elevation of the Iberian Peninsula? What is the quantitative contribution to topography induced by the intraplate tectonics of Iberia? How was this intraplate deformation in the middle of the Iberian microplate triggered? To answer these questions, I first gathered information about the tectonic events in Iberia during the Cenozoic from previous structural tectonic and geodynamic modelling publications. Continental collision with Eurasia in the north first gave rise to the uprising of the Pyrenean and Basque-Cantabrian chains. Deformation subsequently jumped southwards and formed the elevation of the interior mountain ranges. Meanwhile in the southern margin, the subduction of the Tethys oceanic lithosphere due to the Africa-Iberia convergence gave rise to the Betics and opened the Alborán Sea. The underlaying hypothesis of this thesis is that this succession can be reproduced via a geodynamic model giving the appropriate initial conditions that are in reasonable agreement with the geological setting during the early-Cenozoic Iberia.
To this purpose, we carried out a series of high-resolution mechanical and thermomechanical numerical models with a state-of-the-art code named UNDERWORLD 2.0 (still under development at Univ. Melbourne). We first review fundamental ideas such as the patterns of deformation of the lithosphere predicted for converging continental margins, as well as the elevation of mountain ranges in a continental collision scenario. Then we investigate how the crustal deformation accommodates far from the continental margins, taking into account the mathematical equations and physical laws that govern the thermal field and rock deformation. Based on these, a series of mechanical numerical models are developed to explore the possible evolutionary scenarios after a continental collision. Two deformation end member models appear: double-vergence and crustal folding.
While in the first one deformation concentrates near the axial collision zone where the orogen develops, in the second, deformation is transmitted farther from the initial contact between lithospheres. We compare these results with patterns of deformation seen in the Pyrenean mountain range as well as other natural scenarios where cortical folding occurs near a thrust failure like in the Zagros Chain in Iran.
This thesis then focuses on a series of high-resolution 2D numerical models for the North-Central area of the Peninsula. These models aim at linking the Cenozoic evolution of the Cantabrian chain to that of the Central System and the Duero basin. Here, deformation and failure consider creep-like behavior and plasticity in a viscoplastic rheology. We test the hypothesis of the presence of a detachment level within the Variscan basement, at the lower crust, of limited srength and thus capable of transmitting deformation towards the interior, potentially leading to the rise of the Central System. An alternative tested hypothesis is that the entire lithosphere folded in response to the convergence between Iberia and Eurasia.
Finally, we extend these 2D numerical models to the southern margin of Iberia to investigate how the approximation of Africa may have affected the distribution and timing of shortening in the different domains of the microplate, with particular emphasis on the topography and deformation of the Central System and adjacent basins.