Evolution and diversity of subduction zones controlled by slab width

Abstract

Subducting slabs provide the main driving force for plate motion and flow in the Earth's mantle, and geodynamic, seismic and geochemical studies offer insight into slab dynamics and subduction-induced flow. Most previous geodynamic studies treat subduction zones as either infinite in trench-parallel extent (that is, two-dimensional) or finite in width but fixed in space. Subduction zones and their associated slabs are, however, limited in lateral extent (250-7,400 km) and their three-dimensional geometry evolves over time. Here we show that slab width controls two first-order features of plate tectonics-the curvature of subduction zones and their tendency to retreat backwards with time. Using three-dimensional numerical simulations of free subduction, we show that trench migration rate is inversely related to slab width and depends on proximity to a lateral slab edge. These results are consistent with retreat velocities observed globally, with maximum velocities (6-16 cm yr(-1)) only observed close to slab edges (<1,200 km), whereas far from edges (>2,000 km) retreat velocities are always slow (<2.0 cm yr(-1)). Models with narrow slabs (< or =1,500 km) retreat fast and develop a curved geometry, concave towards the mantle wedge side. Models with slabs intermediate in width ( approximately 2,000-3,000 km) are sublinear and retreat more slowly. Models with wide slabs (> or =4,000 km) are nearly stationary in the centre and develop a convex geometry, whereas trench retreat increases towards concave-shaped edges. Additionally, we identify periods (5-10 Myr) of slow trench advance at the centre of wide slabs. Such wide-slab behaviour may explain mountain building in the central Andes, as being a consequence of its tectonic setting, far from slab edges.

Rheologic controls on slab dynamics

“…Models with stronger slabs and slow slab rollback (1 cm/yr) do have shallower slab dips [Cížková et al, 2002]. In addition, 3-D models show that roll-back rate depends on the length of the subduction zone, with short subduction zones exhibiting fast rollback, while the central regions of long subduction zones are stationary [Schellart et al, 2007]. Together with previous 3-D laboratory models [e.g., Funiciello et al, 2003;Bellahsen et al, 2005;Piromallo et al, 2006], Schellart et al [2007] demonstrate the importance of toroidal flow for slab dynamics near slab edges.…”

“…[53] Finally, trench migration is clearly an important factor in several subductions zones, and may be the dominant control on slab dynamics for slabs of short lateral extent, where toroidal flow around the edge of the slab has a strong influence on slab dynamics Stegman et al, 2006;Royden and Husson, 2006;Schellart et al, 2007]. Small slab dips at early stages of subduction are also likely to be controlled by slab roll-back [Gurnis et al, 2004].…”

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].…”

“…[19] Tectonic models invoking mantle-level processes related to slab rollback are widely used to explain arc curvature and back-arc rifting [e.g., Schellart and Lister, 2004;Schellart et al, 2007]. 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).…”

Kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern Mediterranean region since the late Cretaceous

“…Another parameter to consider is the slab width. Indeed, the resisting forces of the mantle to slab roll-back are higher with a wide slab [Faccenna et al, 2007;Schellart et al, 2007;Loiselet et al, 2009], such as in the late…”