Kinematics of subduction and subduction‐induced flow in the upper mantle

Abstract

[1] Results of fluid dynamical experiments are presented to model the kinematics of lithospheric subduction in the upper mantle. The experiments model a dense highviscosity plate (subducting lithosphere) overlying a less dense low-viscosity layer (upper mantle). The overriding lithosphere is not incorporated. Several important features of slab behavior were investigated including the temporal variability of hinge line migration, the kinematic behavior of the slab and the subduction-induced upper mantle flow. Both fixed and free trailing edge boundary conditions of the subducting plate were investigated. Results show that hinge line retreat is a natural consequence of subduction of a negatively buoyant slab. The migration rate increases until the slab approaches the upper-lower mantle discontinuity, resulting in a decrease in migration rate followed by a renewed increase and finally approaching a steady state. Slab retreat results in mantle flow, with material initially located underneath the slab flowing around the lateral slab edges toward the mantle wedge. Experimental results indicate that all rollback-induced flow occurs around the lateral slab edges, forcing the hinge line to attain a convex shape toward the direction of retreat. No signs for poloidal flow underneath the slab tip have been detected. Only a small component of toroidal-type flow was observed underneath slanting slab tips. For a fixed trailing edge, the slab does not sink vertically downward, but sinks at an angle in a regressive manner. For a free trailing edge, slab sinking is oriented more vertically while the surface part of the subducting plate is pulled into the subduction zone.

Collisional model for rapid fore‐arc block rotations, arc curvature, and episodic back‐arc rifting in subduction settings

“…Although we agree that deep-seated processes related to slab rollback are important for understanding these fundamental convergent margin processes, our compilation in Figure 5 demonstrates that crustal-level collisional processes play a dominant role based on the close spatial and temporal coincidence between collisional events and rotation and rifting events ( Figure 5, Table 1, and Appendix A). These linked processes are not explained by models invoking slab rollback alone [Schellart and Lister, 2004;Schellart, 2004;Schellart et al, 2007].…”

“…[43] Advocates of mantle-controlled 2-D models for back-arc basin opening have proposed shortlived mechanisms that could produce the observed style of episodic opening, namely, (1) slab detachment [Faccenna et al, 2006] or (2) the intersection of the subducted slab with the 660-km-deep transition zone between the upper and lower mantle [Faccenna et al, 2001a[Faccenna et al, , 2001bSchellart, 2004]. However, it is not yet proven that these mechanisms actually are responsible for back-arc episodicity.…”

“…Although some degree of rollback of the negatively buoyant oceanic slab is likely, we suspect that extremely high rates of rollback are unlikely to occur, as significant viscous resistance will occur in the mantle as the slab attempts to ''sweep'' or ''fall'' through the mantle [e.g., Scholz and Campos, 1995]. Laboratory analog models of the subduction process that reproduce slab rollback at high rates (up to 14 cm/a [Schellart, 2004[Schellart, , 2005Funiciello et al, 2004]) suffer from the fact that they do not include an upper plate. This is a problem because mantle corner flow eddies induced by the subduction process create viscous traction forces that hold the upper and lower plates together [e.g., Jischke, 1975;Winder and Peacock, 2001;Conrad and Lithgow-Bertelloni, 2004].…”

“…Such a model requires the presence of a slab edge or a lateral change in the age of the subducting plate [e.g., Schellart, 2004;Schellart et al, 2002Schellart et al, , 2007 to produce an along-strike change in rate of rollback of the lower plate. Recent global compilations show that rollback rates do not correlate with the age and density of an oceanic slab [e.g., Lallemand et al, 2005], nor do variations in rollback rate correlate with along-strike variations in subducting slab age.…”

The dynamics of laterally variable subductions: laboratory models applied to the Hellenides

“…The roll-back of slabs causes the development of toroidal cells at slab edges (Dvorkin, 1993;Funiciello et al, 2004;Schellart, 2004;Funiciello et al, 2006;Piromallo et al, 2006). In the model, the persistent rollback of the oceanic lithosphere to the south excites such a mantle flow that opposes the roll-back of the northern continental lithosphere, which explains the decreasing v t , and even slight advance, to the north.…”