Influence of geometry and eclogitization on oceanic plateau subduction

Abstract

Subduction is driven by the negative buoyancy of the slab, which depends on both the temperature and composition of the lithospheric plate. In the case of subduction of an oceanic plateau, larger thickness of the lower-density crust and harzburgite layers can locally decrease the negative buoyancy available to drive subduction. However, the ability of a plateau to have an impact on subduction depends on the total buoyancy of the slab, and therefore also depends on size of the plateau and the basalt to eclogite transition, which substantially increases the density of the crust. Using 2-D numerical finite element models of subduction, we investigate the role of eclogitization and oceanic plateau size (thickness and length) in the process of oceanic plateau subduction. Model results show that eclogitization of the crust substantially increases the chances that a plateau will be subducted because the extra buoyancy of larger plateaus is lost through the phase transition. For kinematically driven models, all plateaus are subducted regardless of the thickness or width. Extrapolation of these results to 3-D geometry shows that sufficient slab buoyancy is available to sustain subduction for narrow plateaus with slab widths 6–7 times the plateau width (depending on plateau thickness and length). In dynamically driven models, subduction of oceanic plateaus of various sizes can substantially slow subduction, and large plateaus (>200km long and >25km thick) can lead to break-off of the slab and underplating of the plateau.