CONSTRAINTS ON SUBDUCTION GEODYNAMICS FROM SEISMIC ANISOTROPY

Abstract Much progress has been made over the past several decades in delineating the structure of subducting slabs, but several key aspects of their dynamics remain poorly constrained. Major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology, slab hydration and dehydration, mechanical coupling between slabs and the ambient mantle, the geometry of mantle flow above and beneath slabs, and the interactions between slabs and deep discontinuities such as the core‐mantle boundary. Observations of seismic anisotropy can provide relatively direct constraints on mantle dynamics because of the link between deformation and the resulting anisotropy: when mantle rocks are deformed, a preferred orientation of individual mineral crystals or materials such as partial melt often develops, resulting in the directional dependence of seismic wave speeds. Measurements of seismic anisotropy thus represent a powerful tool for probing mantle dynamics in subduction systems. Here I review the observational constraints on seismic anisotropy in subduction zones and discuss how seismic data can place constraints on wedge, slab, and sub‐slab anisotropy. I also discuss constraints from mineral physics investigations and geodynamical modeling studies and how they inform our interpretation of observations. I evaluate different models in light of constraints from seismology, geodynamics, and mineral physics. Finally, I discuss some of the major unsolved problems related to the dynamics of subduction systems and how ongoing and future work on the characterization and interpretation of seismic anisotropy can lead to progress, particularly in frontier areas such as understanding slab dynamics in the deep mantle.