Mantle flow in subduction systems: The mantle wedge flow field and implications for wedge processes

Abstract

[1] The mantle wedge above subducting slabs is associated with many important processes, including the transport of melt and volatiles. Our understanding of mantle wedge dynamics is incomplete, as the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, measurements of shear wave splitting can constrain the geometry of mantle flow. In order to identify processes that make first-order contributions to the pattern of wedge flow, we have compiled a data set of local S splitting measurements from mantle wedges worldwide. There is a large amount of variability in splitting parameters, with average delay times ranging from~0.1 to 0.3 s up to~1.0-1.5 s and large variations in fast directions. We tested for relationships between splitting parameters and a variety of parameters related to subduction processes. We also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.

Lattice-Preferred orientations of olivine in subducting oceanic lithosphere derived from the observed seismic anisotropies in double seismic zones

“…There are large variations in average delay times for these slab zones, with some zones exhibiting relatively weak seismic anisotropy (e.g., JAP and SMA DSZs) and some others exhibiting delay times up to *2 s (e.g., JAV1 and KUR DSZs). This is consistent with the complex spatial variations of shear wave splitting patterns in most mantle wedges worldwide concluded by Long and Wirth (2013). The correlations of the average delay time dt with convergence rate V c , as well with DSZ's subduction angle a DSZ , were analyzed (Fig.…”

Evidence for trench-parallel mantle flow in the northern Cascade Arc from basalt geochemistry

“…However, seismic anisotropy data, 3-D numerical modeling, and experimental studies have shown that mantle flow in subduction zones may be much more complex, especially at and near the terminations of the arcs (Kneller and van Keken, 2008;Long and Silver, 2009;Long and Wirth, 2013;MacDougall et al, 2014;Schellart, 2010Schellart, , 2004. Because the compositions of primary arc magmas reflect the composition of the mantle wedge (variably modified by slabderived components), spatial variations in the geochemistry of arc magmas provide independent evidence for circulation patterns in the mantle wedge.…”

Erratum to: Crystal preferred orientations of olivine, orthopyroxene, serpentine, chlorite, and amphibole, and implications for seismic anisotropy in subduction zones: a review

“…1) (Savage, 1999;Park and Levin, 2002;Long and Silver, 2008;Long, 2013;Long and Wirth, 2013;Wang and Zhao, 2013;Zhao et al, 2016). Trench-parallel seismic anisotropy of the fast Swave was observed in many fore-arc areas and sub-slabs in subduction zones (Ando et al, 1983;Fouch and Fischer, 1996;Margheriti et al, 1996;Smith et al, 2001;Nakajima and Hasegawa, 2004;Long and van der Hilst, 2005;Abt et al, 2010;Long and Becker, 2010;Di Leo et al, 2012;Long and Wirth, 2013;Wagner Figure 9 (after Jung et al, 2010). The east-west direction corresponds to the lineation (L), and the north-south corresponds to the foliation normal.…”

“…It is interesting to see the changes in seismic anisotropy patterns; from trench-parallel S-wave anisotropy in the fore-arc area to the trench-normal S-wave anisotropy in the back-arc area (Smith et al, 2001;Nakajima and Hasegawa, 2004;Long and van der Hilst, 2006;Long and Wirth, 2013). This pattern of seismic anisotropy may be explained by the change in olivine CPO from Type-B in the fore-arc to Type-A, -C (or -E) in the back-arc (Kneller et al, 2005;Katayama and Karato, 2006;Kneller et al, 2007;Karato et al, 2008;Jung, 2012).…”

“…3). Those hydrous minerals are also known as elastically anisotropic minerals (Aleksandrov and Ryzhova, 1961a;Mainprice and Ildefonse, 2009;Bezacier et al, 2010;Mookherjee (Long and Wirth, 2013). Arrows indicate the first-order patterns in average fast direction; where multiple arrows are present, this indicates a spatial transition in observed orientation ().…”