Seismic anisotropy and mantle flow below subducting slabs

TitleSeismic anisotropy and mantle flow below subducting slabs
Publication TypeJournal Article
Year of Publication2017
AuthorsWalpole J., Wookey J., Kendall J.M, Masters T.G
JournalEarth and Planetary Science Letters
Volume465
Pagination155-167
Date Published2017/05
Type of ArticleArticle
ISBN Number0012-821X
Accession NumberWOS:000400202600015
Keywordsasthenosphere; cluster-analysis; elastic-anisotropy; finite strain; high-pressure; lattice-preferred orientation; lower mantle; Mantle convection; oceanic plates; seismic anisotropy; Shear; shear wave splitting; subduction; transition zone; trench parallel flow; uppermost; wave splitting measurements
Abstract

Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning similar to 40,000 km of subduction zone trenches - over the complete range of available source depths (4 to 687 km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth <50km) - suggesting a separate region of anisotropy in the lithospheric slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite. Crown Copyright (C) 2017 Published by Elsevier B.V. All rights reserved.

DOI10.1016/j.epsl.2017.02.023
Short TitleEarth Planet. Sci. Lett.
Student Publication: 
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