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Mid-mantle anisotropy in subduction zones and deep water transport

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Mid-mantle anisotropy in subduction zones and deep water transport. / Nowacki, Andy; Kendall, J-Michael; Wookey, James; Pemberton, Asher.

In: Geochemistry, Geophysics, Geosystems, Vol. 16, No. 3, 15.04.2015, p. 764-784.

Research output: Contribution to journalArticle

Harvard

Nowacki, A, Kendall, J-M, Wookey, J & Pemberton, A 2015, 'Mid-mantle anisotropy in subduction zones and deep water transport', Geochemistry, Geophysics, Geosystems, vol. 16, no. 3, pp. 764-784. https://doi.org/10.1002/2014GC005667

APA

Nowacki, A., Kendall, J-M., Wookey, J., & Pemberton, A. (2015). Mid-mantle anisotropy in subduction zones and deep water transport. Geochemistry, Geophysics, Geosystems, 16(3), 764-784. https://doi.org/10.1002/2014GC005667

Vancouver

Nowacki A, Kendall J-M, Wookey J, Pemberton A. Mid-mantle anisotropy in subduction zones and deep water transport. Geochemistry, Geophysics, Geosystems. 2015 Apr 15;16(3):764-784. https://doi.org/10.1002/2014GC005667

Author

Nowacki, Andy ; Kendall, J-Michael ; Wookey, James ; Pemberton, Asher. / Mid-mantle anisotropy in subduction zones and deep water transport. In: Geochemistry, Geophysics, Geosystems. 2015 ; Vol. 16, No. 3. pp. 764-784.

Bibtex

@article{748c972e130646f886d1fa921f4d155d,
title = "Mid-mantle anisotropy in subduction zones and deep water transport",
abstract = "The Earth's transition zone has until recently been assumed to be seismically 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 updip 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.",
keywords = "deep earthquakes, DHMS, mantle flow, shear wave splitting, subduction, transition zone",
author = "Andy Nowacki and J-Michael Kendall and James Wookey and Asher Pemberton",
year = "2015",
month = "4",
day = "15",
doi = "10.1002/2014GC005667",
language = "English",
volume = "16",
pages = "764--784",
journal = "Geochemistry, Geophysics, Geosystems",
issn = "1525-2027",
publisher = "American Geophysical Union",
number = "3",

}

RIS - suitable for import to EndNote

TY - JOUR

T1 - Mid-mantle anisotropy in subduction zones and deep water transport

AU - Nowacki, Andy

AU - Kendall, J-Michael

AU - Wookey, James

AU - Pemberton, Asher

PY - 2015/4/15

Y1 - 2015/4/15

N2 - The Earth's transition zone has until recently been assumed to be seismically 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 updip 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.

AB - The Earth's transition zone has until recently been assumed to be seismically 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 updip 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.

KW - deep earthquakes

KW - DHMS

KW - mantle flow

KW - shear wave splitting

KW - subduction

KW - transition zone

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U2 - 10.1002/2014GC005667

DO - 10.1002/2014GC005667

M3 - Article

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SP - 764

EP - 784

JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

SN - 1525-2027

IS - 3

ER -