Seismological Evidence for Girdled Olivine Lattice-Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading

J. B. Russell; J. B. Gaherty; H. F. Mark; G. Hirth; L. N. Hansen; D. Lizarralde; J. A. Collins; R. L. Evans

doi:10.1029/2022GC010542

Seismological Evidence for Girdled Olivine Lattice-Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading

J. B. Russell, J. B. Gaherty, H. F. Mark, G. Hirth, L. N. Hansen, D. Lizarralde, J. A. Collins, R. L. Evans

Earth and Environmental Sciences-Twin Cities

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

Seismic anisotropy produced by aligned olivine in oceanic lithosphere offers a window into mid-ocean ridge (MOR) dynamics. Yet, interpreting anisotropy in the context of grain-scale deformation processes and strain observed in laboratory experiments and natural olivine samples has proven challenging due to incomplete seismological constraints and length scale differences spanning orders of magnitude. To bridge this observational gap, we estimate an in situ elastic tensor for oceanic lithosphere using co-located compressional- and shear-wavespeed anisotropy observations at the NoMelt experiment located on ∼70 Ma seafloor. The elastic model for the upper 7 km of the mantle, NoMelt_SPani7, is characterized by a fast azimuth parallel to the fossil-spreading direction, consistent with corner-flow deformation fabric. We compare this model with a database of 123 petrofabrics from the literature to infer olivine crystallographic orientations and shear strain accumulated within the lithosphere. Direct comparison to olivine deformation experiments indicates strain accumulation of 250%–400% in the shallow mantle. We find evidence for D-type olivine lattice-preferred orientation (LPO) with fast [100] parallel to the shear direction and girdled [010] and [001] crystallographic axes perpendicular to shear. D-type LPO implies similar amounts of slip on the (010)[100] and (001)[100] easy slip systems during MOR spreading; we hypothesize that grain-boundary sliding during dislocation creep relaxes strain compatibility, allowing D-type LPO to develop in the shallow lithosphere. Deformation dominated by dislocation-accommodated grain-boundary sliding (disGBS) has implications for in situ stress and grain size during MOR spreading and implies grain-size dependent deformation, in contrast to pure dislocation creep.

Original language	English (US)
Article number	e2022GC010542
Journal	Geochemistry, Geophysics, Geosystems
Volume	23
Issue number	10
DOIs	https://doi.org/10.1029/2022GC010542
State	Published - Oct 2022

Bibliographical note

Funding Information:
The authors thank Haemyeong Jung, Katsuyoshi Michibayashi, and Misha Bystricky who shared previously published elastic tenors used in this study. The authors thank Andréa Tommasi and two anonymous reviewers whose thoughtful comments helped greatly improve this article. This work also benefited from conversations with Benjamin Holtzman. This research was supported by the NSF under Grant OCE‐0928270 and OCE‐1538229 (J.B. Gaherty).

Funding Information:
The authors thank Haemyeong Jung, Katsuyoshi Michibayashi, and Misha Bystricky who shared previously published elastic tenors used in this study. The authors thank Andréa Tommasi and two anonymous reviewers whose thoughtful comments helped greatly improve this article. This work also benefited from conversations with Benjamin Holtzman. This research was supported by the NSF under Grant OCE-0928270 and OCE-1538229 (J.B. Gaherty).

Publisher Copyright:
© 2022. The Authors.

Keywords

grain-boundary sliding
mid-ocean ridge
oceanic lithosphere
seafloor spreading
seismic anisotropy
surface waves

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Russell, J. B., Gaherty, J. B., Mark, H. F., Hirth, G., Hansen, L. N., Lizarralde, D., Collins, J. A., & Evans, R. L. (2022). Seismological Evidence for Girdled Olivine Lattice-Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading. Geochemistry, Geophysics, Geosystems, 23(10), Article e2022GC010542. https://doi.org/10.1029/2022GC010542

Seismological Evidence for Girdled Olivine Lattice-Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading. / Russell, J. B.; Gaherty, J. B.; Mark, H. F. et al.
In: Geochemistry, Geophysics, Geosystems, Vol. 23, No. 10, e2022GC010542, 10.2022.

Research output: Contribution to journal › Article › peer-review

Russell, JB, Gaherty, JB, Mark, HF, Hirth, G, Hansen, LN, Lizarralde, D, Collins, JA & Evans, RL 2022, 'Seismological Evidence for Girdled Olivine Lattice-Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading', Geochemistry, Geophysics, Geosystems, vol. 23, no. 10, e2022GC010542. https://doi.org/10.1029/2022GC010542

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abstract = "Seismic anisotropy produced by aligned olivine in oceanic lithosphere offers a window into mid-ocean ridge (MOR) dynamics. Yet, interpreting anisotropy in the context of grain-scale deformation processes and strain observed in laboratory experiments and natural olivine samples has proven challenging due to incomplete seismological constraints and length scale differences spanning orders of magnitude. To bridge this observational gap, we estimate an in situ elastic tensor for oceanic lithosphere using co-located compressional- and shear-wavespeed anisotropy observations at the NoMelt experiment located on ∼70 Ma seafloor. The elastic model for the upper 7 km of the mantle, NoMelt_SPani7, is characterized by a fast azimuth parallel to the fossil-spreading direction, consistent with corner-flow deformation fabric. We compare this model with a database of 123 petrofabrics from the literature to infer olivine crystallographic orientations and shear strain accumulated within the lithosphere. Direct comparison to olivine deformation experiments indicates strain accumulation of 250%–400% in the shallow mantle. We find evidence for D-type olivine lattice-preferred orientation (LPO) with fast [100] parallel to the shear direction and girdled [010] and [001] crystallographic axes perpendicular to shear. D-type LPO implies similar amounts of slip on the (010)[100] and (001)[100] easy slip systems during MOR spreading; we hypothesize that grain-boundary sliding during dislocation creep relaxes strain compatibility, allowing D-type LPO to develop in the shallow lithosphere. Deformation dominated by dislocation-accommodated grain-boundary sliding (disGBS) has implications for in situ stress and grain size during MOR spreading and implies grain-size dependent deformation, in contrast to pure dislocation creep.",

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note = "Funding Information: The authors thank Haemyeong Jung, Katsuyoshi Michibayashi, and Misha Bystricky who shared previously published elastic tenors used in this study. The authors thank Andr{\'e}a Tommasi and two anonymous reviewers whose thoughtful comments helped greatly improve this article. This work also benefited from conversations with Benjamin Holtzman. This research was supported by the NSF under Grant OCE‐0928270 and OCE‐1538229 (J.B. Gaherty). Funding Information: The authors thank Haemyeong Jung, Katsuyoshi Michibayashi, and Misha Bystricky who shared previously published elastic tenors used in this study. The authors thank Andr{\'e}a Tommasi and two anonymous reviewers whose thoughtful comments helped greatly improve this article. This work also benefited from conversations with Benjamin Holtzman. This research was supported by the NSF under Grant OCE-0928270 and OCE-1538229 (J.B. Gaherty). Publisher Copyright: {\textcopyright} 2022. The Authors.",

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AU - Evans, R. L.

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Seismological Evidence for Girdled Olivine Lattice-Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading

Abstract

Bibliographical note

Keywords

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