Impact of the overriding plate crustal rheology on convergence zones dynamics
Abstract
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
the convergence zones, the deformation is classically classified as
follows: i) 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, ii)
convergence between an oceanic and a continental lithosphere,
which is generally accommodated by subduction and can also
lead to the formation of a mountains range at the plate boundary
and iii) convergence between two continental lithospheres leading
to the formation of a collisional mountain range formed by the
stacking of crustal slices. Hence, different materials (i.e., oceanic
crust, continental crust, sediments) evolving in different contexts
(i.e., oceanic subduction, continental subduction, obduction) result
in the formation of contrasted structures in terms of units
size, morphology and metamorphism. In addition, some convergent
zones from a similar tectonic context (e.g., ocean/continent
convergence) can produce mountains ranges presenting very different
characteristics (e.g., characterized by extension as in the
Aegean or, at the opposite, by significant shortening, as in the
Andes). Although the mechanism of plate convergence appears
to be the same, the structures obtained at the surface (e.g., Alpes,
Andes, Aegean, Himalayas) seem then to be unique. Rheology of
both the lower subducting plate and of the plates 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 and, more precisely, on the role of
the crustal part. For this, we use both 2D thermo-mechanical numerical
models and 3D analogue models, in which the rheological
property of the crust of the upper plate is tested vertically but
also laterally. This complementary approach allows us to test the
effect of numerous parameters controlling the rheological structure
(e.g., nature of the material, thickness, convergence velocity,
initial thermal structure) on the convergence zone dynamics and
on the deformation style occurring at plate boundaries