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Subduction‐induced mantle flow, finite strain, and seismic anisotropy: Numerical modeling
Author(s) -
Li ZhongHai,
Di Leo Jeanette F.,
Ribe Neil M.
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2014jb010996
Subject(s) - geology , mantle wedge , subduction , mantle (geology) , slab , seismic anisotropy , shear wave splitting , transition zone , geophysics , trench , seismology , finite strain theory , tectonics , finite element method , physics , materials science , layer (electronics) , thermodynamics , composite material
Surface measurements of shear wave splitting patterns are widely used to infer the mantle circulation around subducting slabs; however, the relation between mantle flow and seismic anisotropy is still elusive. Finite strain is a direct measurement of time‐dependent deformation and has been proposed as a proxy for the crystal‐preferred orientation (CPO) of mantle minerals. We have conducted a series of numerical models to systematically investigate the mantle flow, finite strain, olivine CPO, and SKS wave splitting in oceanic subduction zones with variable slab width. They demonstrate that the preferred orientations of olivine a axes generally agree with the long (extensional) axes of the finite strain ellipsoid (FSE), even in these very complex mantle flow fields; however, neither the a axis nor the FSE axes necessarily aligns with the instantaneous mantle velocity vector. We identify two domains with distinct deformation mechanisms in the central subplate mantle, where simple shear induced by plate advance dominates at shallow depths and produces trench‐normal fast splitting, while pure shear induced by slab rollback dominates the deeper mantle and results in trench‐parallel fast splitting. The SKS splitting patterns are thus dependent on the competing effects of these two mechanisms and also on the subduction partition ratio γ = X p / X t : trench parallel when γ < 1 and trench normal when γ >1. In addition, different mantle deformation mechanisms and SKS splitting patterns are observed in the mantle wedge and around the slab edges, which may aid in the general interpretation of seismic anisotropy observations in natural subduction zones.