Abstract
Abstract. Continental collision is an intrinsic feature of plate tectonics. The closure of an oceanic basin leads to the onset of subduction of buoyant continental material, which slows down and eventually stops the subduction process. In natural cases, evidence of advancing margins has been recognized in continental collision zones such as India-Eurasia and Arabia-Eurasia. We perform a parametric study of the geometrical and rheological influence on subduction dynamics during the subduction of continental lithosphere. In our 2-D numerical models of a free subduction system with temperature and stress-dependent rheology, the trench and the overriding plate move self-consistently as a function of the dynamics of the system (i.e. no external forces are imposed). This setup enables to study how continental subduction influences the trench migration. We found that in all models the slab starts to advance once the continent enters the subduction zone and continues to migrate until few million years after the ultimate slab detachment. Our results support the idea that the advancing mode is favoured and, in part, provided by the intrinsic force balance of continental collision. We suggest that the advance is first induced by the locking of the subduction zone and the subsequent steepening of the slab, and next by the sinking of the deepest oceanic part of the slab, during stretching and break-off of the slab. These processes are responsible for the migration of the subduction zone by triggering small-scale convection cells in the mantle that, in turn, drag the plates. The amount of advance ranges from 40 to 220 km and depends on the dip angle of the slab before the onset of collision.
Highlights
Slab pull caused by the negative buoyancy of subducting oceanic lithosphere represents a main driving contribution for plate motion (e.g. Elsasser, 1969; Forsyth and Uyeda, 1975)
We investigate the dynamic behaviour of the slab and the margin between the plates during continental collision without any external forces, i.e. driven entirely by the changes in the force balance due to the collision process
Our model results show how trenches can start advancing when continental collision occurs. These results are consistent with natural collisional zones such as Arabia-Eurasia and India-Eurasia, where the advancing style is recorded in geological features
Summary
Slab pull caused by the negative buoyancy of subducting oceanic lithosphere represents a main driving contribution for plate motion (e.g. Elsasser, 1969; Forsyth and Uyeda, 1975). Slab pull caused by the negative buoyancy of subducting oceanic lithosphere represents a main driving contribution for plate motion Cloos, 1993; Chemenda et al, 1996; Kerr and Tarney, 2005; Vos et al, 2007) or (3) the slab breaks off as a consequence of tensile stress from the pull of the sinking oceanic lithosphere in the mantle connected to the continental part of the plate De Franco et al (2008) suggested that the geometry of the incoming continental plate, the tectonic setting, the rheology and the length of the sinking oceanic plate control whether the incoming crust subducts entirely, separates partially or entirely from the lithospheric mantle or blocks the trench, likely leading to slab break-off Which scenario takes place depends on several factors including convergence rate, thickness, rheological and physical composition and thermal structure of the continental lithosphere (van den Beukel and Wortel, 1987). De Franco et al (2008) suggested that the geometry of the incoming continental plate, the tectonic setting, the rheology and the length of the sinking oceanic plate control whether the incoming crust subducts entirely, separates partially or entirely from the lithospheric mantle or blocks the trench, likely leading to slab break-off.
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