Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading
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 ch...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Wiley
2022-10-01
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| Series: | Geochemistry, Geophysics, Geosystems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2022GC010542 |
| _version_ | 1797638054773522432 |
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| author | J. B. Russell J. B. Gaherty H. F. Mark G. Hirth L. N. Hansen D. Lizarralde J. A. Collins R. L. Evans |
| author_facet | J. B. Russell J. B. Gaherty H. F. Mark G. Hirth L. N. Hansen D. Lizarralde J. A. Collins R. L. Evans |
| author_sort | J. B. Russell |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-03-11T12:57:12Z |
| format | Article |
| id | doaj.art-121da204978f4d149220ecefc22059c5 |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-11T12:57:12Z |
| publishDate | 2022-10-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-121da204978f4d149220ecefc22059c52023-11-03T16:56:07ZengWileyGeochemistry, Geophysics, Geosystems1525-20272022-10-012310n/an/a10.1029/2022GC010542Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor SpreadingJ. B. Russell0J. B. Gaherty1H. F. Mark2G. Hirth3L. N. Hansen4D. Lizarralde5J. A. Collins6R. L. Evans7Department of Earth, Environmental and Planetary Sciences Brown University Providence RI USASchool of Earth and Sustainability Northern Arizona University Flagstaff AZ USAWoods Hole Oceanographic Institution Woods Hole MA USADepartment of Earth, Environmental and Planetary Sciences Brown University Providence RI USADepartment of Earth and Environmental Sciences University of Minnesota Minneapolis MN USAWoods Hole Oceanographic Institution Woods Hole MA USAWoods Hole Oceanographic Institution Woods Hole MA USAWoods Hole Oceanographic Institution Woods Hole MA USAAbstract 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.https://doi.org/10.1029/2022GC010542oceanic lithosphereseismic anisotropymid‐ocean ridgesurface wavesseafloor spreadinggrain‐boundary sliding |
| spellingShingle | J. B. Russell J. B. Gaherty H. F. Mark G. Hirth L. N. Hansen D. Lizarralde J. A. Collins R. L. Evans Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading Geochemistry, Geophysics, Geosystems oceanic lithosphere seismic anisotropy mid‐ocean ridge surface waves seafloor spreading grain‐boundary sliding |
| title | Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading |
| title_full | Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading |
| title_fullStr | Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading |
| title_full_unstemmed | Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading |
| title_short | Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading |
| title_sort | seismological evidence for girdled olivine lattice preferred orientation in oceanic lithosphere and implications for mantle deformation processes during seafloor spreading |
| topic | oceanic lithosphere seismic anisotropy mid‐ocean ridge surface waves seafloor spreading grain‐boundary sliding |
| url | https://doi.org/10.1029/2022GC010542 |
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