Evolution of subduction-induced mantle flow around the slab edges in analog models of free subduction
Abstract
Mantle flow around subduction zones is though to be strongly controlled by the dynamics of subducting plates. Its role is important because it can in turn have an effect on the subduction process, for instance by deforming the overriding plate or by curving the slab of relatively narrow subduction zones. In addition subduction is known to be a complex 3-D process and the associated mantle flow is therefore supposed to vary both in intensity and direction depending on its location. Particularly, recent seismic anisotropy, laboratory and numerical studies have evidenced a complex 3-D geometry of the mantle flow around the slab edges involving poloidal and toroidal components. But how this 3-D flow pattern develops and evolves in relation with the subducting plate dynamics remains to be solved. To answer this question we performed analog models of free subduction and we tracked the evolution of the associated upper mantle flow in the vicinity of lateral slab edges. For this purpose we used a particle image velocimetry technique that allowed the quantification of mantle flow velocity in both horizontal and vertical direction in several horizontal or vertical sections. Our generic models indicate that subduction-induced mantle flow around the slab edges is four-dimensional as evidenced by previous analog and numerical studies. Slab rollback induces mantle circulation from the sub-slab region toward the mantle wedge. We found that the toroidal flow is vigorous with a steady maximum velocity of up to 80% of the steady trench retreat velocity. We also evidenced the occurrence of a large upwelling area located far from the sub-slab region (in a direction parallel to the trench) with a steady maximum velocity of about 20% of the steady trench retreat rate. The maximum vertical extent of this area is of about 450 km at 150 km from the slab edge. The generic experiments therefore suggest that the toroidal component of the subduction-induced mantle flow can be strong and could have an important impact on all processes occurring around slab edges. The large area of upwelling located far from the sub-slab region (in a direction parallel to the trench) could induce decompression melting and thus could be the source of certain types of intraplate volcanism.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMDI23B..03S
- Keywords:
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- 8170 TECTONOPHYSICS Subduction zone processes