Nowacki, A, Kendall, J-M, Wookey, J et al. (1 more author) (2015) Mid-mantle anisotropy in subduction zones and deep water transport. Geochemistry, Geophysics, Geosystems, 16 (3). 764 - 784. ISSN 1525-2027
Abstract
The Earth’s transition zone has until recently been assumed to be seismi-cally isotropic. Increasingly, however, evidence suggests that ordering of material over seismic wavelengths occurs there, but it is unclear what causes this. We use the method of source-side shear wave splitting to examine the anisotropy surrounding earthquakes deeper than 200 km in slabs around the globe. We find significant amounts of splitting (<= 2.4 s), confirming that the transition zone is anisotropic here. However, there is no decrease in the amount of splitting with depth, as would be the case for a metastable tongue of olivine which thins with depth, suggesting this is not the cause. The amount of splitting does not appear to be consistent with processes in the ambient mantle, such as lattice preferred orientation development in wadsleyite, ringwoodite or MgSiO3-perovskite. We invert for the orientation of several mechanisms—subject to uncertainties in mineralogy and deformation—and the best fit is given by up-dip flattening in a style of anisotropy common to hydrous phases and layered inclusions. We suggest that highly anisotropic hydrous phases or hydrated layering is a likely cause of anisotropy within the slab, implying significant water transport from the surface down to at least 660 km depth.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2015. American Geophysical Union. All Rights Reserved. Reproduced in accordance with the publisher's self-archiving policy. |
Keywords: | transition zone; shear wave splitting; DHMS; mantle flow; deep earthquakes; subduction |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 08 Oct 2015 11:37 |
Last Modified: | 23 Jun 2023 21:47 |
Published Version: | http://dx.doi.org/10.1002/2014GC005667 |
Status: | Published |
Publisher: | American Geophysical Union |
Identification Number: | 10.1002/2014GC005667 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:85928 |