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Seismic anisotropy and mantle flow below subducting slabs

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)155–167
Number of pages13
JournalEarth and Planetary Science Letters
Volume465
Early online date22 Mar 2017
DOIs
DateAccepted/In press - 12 Feb 2017
DateE-pub ahead of print - 22 Mar 2017
DatePublished (current) - 1 May 2017

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 ⇠ 40, 000km 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 < 50 km) – 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.

    Research areas

  • Subduction, Seismic Anisotropy, Mantle Convection, Shear Wave Splitting, Trench Parallel Flow, Asthenosphere

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  • Full-text PDF (accepted author manuscript)

    Rights statement: This is the author accepted manuscript (AAM). The final published version (version of record) is available online via Elsevier at http://www.sciencedirect.com/science/article/pii/S0012821X17300912 . Please refer to any applicable terms of use of the publisher.

    Accepted author manuscript, 9.22 MB, PDF document

    Licence: CC BY-NC-ND

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