|Boutelier, D., Chemenda, A. and Jorand, C. 2002. Thermo-mechanical laboratory modelling of continental subduction: first experiments. Schellart, W. P. and Passchier, C. 2002. Analogue modelling of large-scale tectonic processes. Journal of the Virtual Explorer, 7, 61-65.|
Thermo-mechanical laboratory modelling of continental subduction: first experiments
D. Boutelier, A. Chemenda, and C. Jorand
Azur, Universite de Nicé - Sophia Antipolis
Thermo-mechanical physical modelling of continental subduction is performed using new temperature sensitive analogue materials to model the lithospheric layers. The initially horizontal lithosphere model is underlain by the liquid asthenosphere and subjected to a constant vertical thermal gradient. The lithosphere contains three layers: the very weak sedimentary layer, the crust made of a stronger material in which strength reduces with depth due to the temperature increase, and the lithospheric mantle, made of a still stronger material with strength also droping with depth. During subduction, the temperature of all layers increases, causing reduction of their strength and limiting the depth of crustal subduction. The crust subducts to more than 100 km-depth and then undergoes large and complex deformation, including the upward ductile flow of the deeply subducted portions and a localised failure of the upper crust at depth of a few tens of kilometres. This deformation is accompanied by (is part of) the delamination of the crustal and mantle layers which can be stopped by the break off of the subducted continental mantle and the previously subducted oceanic lithosphere. The modelling reveals an interesting burial/exhumation evolution of the sedimentary cover. During initial stages of continental subduction the sediments of the continental margin are dragged to the overriding plate base and are partially accreted at the lower part of the interplate zone (at 60-70 km-depth). These sediments remain there until the beginning of delamination which results in the reduction of the coupling between the crust and the dense mantle, and in the growth of the interplate pressure between the subducted crust and the overriding plate. This pressure squeezes the underplated sediments out. A small amount of these sediments is rapidly extruded along the interplate zone to about 20 km-depth.