Impact of the overriding plate crustalrheology on convergence zones dynamics

National audienceMost of deformation at the Earth’s surface is localized at plateboundaries. This deformation can be accommodated in very differentways depending on the tectonic setting. In the case ofthe convergence zones, the deformation is classically classified asfollows: i) intra-oceanic convergence (when convergence involvestwo 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 alsolead to the formation of a mountains range at the plate boundaryand iii) convergence between two continental lithospheres leadingto the formation of a collisional mountain range formed by thestacking of crustal slices. Hence, different materials (i.e., oceaniccrust, continental crust, sediments) evolving in different contexts(i.e., oceanic subduction, continental subduction, obduction) resultin the formation of contrasted structures in terms of unitssize, morphology and metamorphism. In addition, some convergentzones from a similar tectonic context (e.g., ocean/continentconvergence) can produce mountains ranges presenting very differentcharacteristics (e.g., characterized by extension as in theAegean or, at the opposite, by significant shortening, as in theAndes). Although the mechanism of plate convergence appearsto be the same, the structures obtained at the surface (e.g., Alpes,Andes, Aegean, Himalayas) seem then to be unique. Rheology ofboth the lower subducting plate and of the plates interface isknown to influence the convergence zones dynamics. However,very few studies have addressed the role of the overriding platerheology in details, while it may also exert a large control on thedeformation style at plate boundaries. In this study, we thereforefocus on the influence of the overriding plate rheology on theconvergence zones dynamics and, more precisely, on the role ofthe crustal part. For this, we use both 2D thermo-mechanical numericalmodels and 3D analogue models, in which the rheologicalproperty of the crust of the upper plate is tested vertically butalso laterally. This complementary approach allows us to test theeffect of numerous parameters controlling the rheological structure(e.g., nature of the material, thickness, convergence velocity,initial thermal structure) on the convergence zone dynamics andon the deformation style occurring at plate boundarie