Impact of the overriding plate rheology on convergence zone dynamics.
Résumé
Most of deformation at the Earth’s surface is localized at plate boundaries. This deformation can be accommodated
in very different ways depending on the tectonic setting. In the case of convergence zones, the deformation is
typically simplified and classified as follows:
- intra-oceanic convergence, when convergence involves two oceanic lithospheres, which generally leads to the
subduction/obduction initiation and to the formation of an island arc;
- convergence between an oceanic and a continental lithosphere, which is mainly accommodated by subduction
and can lead to the formation of a mountain range at the plate boundary;
- convergence involving two continental lithospheres, which is accommodated by collision and leads to the
formation of a mountain range produced by the stacking of crustal slices.
Different materials are thus involved (i.e. oceanic crust, continental crust, sediments). Depending on the context
(oceanic or continental subduction), they can form contrasted structures in terms of units size, morphology
and metamorphism (e.g., Alps vs. Andes/Altiplano-Puna). Moreover, some convergent zones with apparently
similar tectonic settings (e.g., continent/continent convergence) show very different patterns of deformation with
either very localized deformation (e.g., the Alps) or, at the opposite, deformation distributed over thousands of
kilometers (e.g, Himalayas/Tibet). Finally, other convergent zones from different tectonic settings seem to show
similar structures (e.g., Tibet plateau and Altiplano-Puna plateaus).
Although the mechanism of plate convergence appears to be the same in each case, the structures obtained
at the surface seem to be unique. Rheology of both the subducting plate and of the plate interface is known to
influence the convergence zones dynamics. However, very few studies have addressed the role of the overriding
plate rheology in details, while it may also exert a large control on the deformation style at plate boundaries.
In this study, we therefore focus on the influence of the overriding plate rheology on the convergence
zones dynamics. For this, we use both 2D and 3D thermo-mechanical numerical models, in which the rheological
properties of both the lithosphere and the crust of the overriding plate are tested vertically but also laterally. This
complementary approach allows us to test the effects of numerous parameters controlling the rheological structure
(i.e. nature of the material, thickness, convergence velocity, initial thermal structure) on the convergence zone
dynamics and on the deformation style occurring at plate boundaries