@article {russell_seismological_2022,
	title = {Seismological Evidence for Girdled Olivine Lattice-Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading},
	journal = {Geochemistry, Geophysics, Geosystems},
	volume = {23},
	number = {10},
	year = {2022},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2022GC010542},
	pages = {e2022GC010542},
	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\%{\textendash}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.},
	keywords = {grain-boundary sliding, mid-ocean ridge, oceanic lithosphere, seafloor spreading, seismic anisotropy, surface waves},
	issn = {1525-2027},
	doi = {10.1029/2022GC010542},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022GC010542},
	author = {Russell, J. B. and Gaherty, J. B. and Mark, H. F. and Hirth, G. and Hansen, L. N. and Lizarralde, D. and Collins, J. A. and Evans, R. L.}
}
@article {russell_lithosphere_2021,
	title = {Lithosphere Structure and Seismic Anisotropy Offshore Eastern North America: Implications for Continental Breakup and Ultra-Slow Spreading Dynamics},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {126},
	number = {12},
	year = {2021},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021JB022955},
	month = {11/2021},
	pages = {e2021JB022955},
	abstract = {The breakup of supercontinent Pangea occurred \~{}200 Ma forming the Eastern North American Margin (ENAM). Yet, the precise timing and mechanics of breakup and onset of seafloor spreading remain poorly constrained. We investigate the relict lithosphere offshore eastern North America using ambient-noise Rayleigh-wave phase velocity (12{\textendash}32 s) and azimuthal anisotropy (17{\textendash}32 s) at the ENAM Community Seismic Experiment (CSE). Incorporating previous constraints on crustal structure, we construct a shear velocity model for the crust and upper \~{}60 km of the mantle beneath the ENAM-CSE. A low-velocity lid (VS of 4.4{\textendash}4.55 km/s) is revealed in the upper 15{\textendash}20 km of the mantle that extends \~{}200 km from the margin, terminating at the Blake Spur Magnetic Anomaly (BSMA). East of the BSMA, velocities are fast (>4.6 km/s) and characteristic of typical oceanic mantle lithosphere. We interpret the low-velocity lid as stretched continental mantle lithosphere embedded with up to \~{}15\% retained gabbro. This implies that the BSMA marks successful breakup and onset of seafloor spreading \~{}170 Ma, consistent with ENAM-CSE active-source studies that argue for breakup \~{}25 Myr later than previously thought. We observe margin-parallel Rayleigh-wave azimuthal anisotropy (2\%{\textendash}4\% peak-to-peak) in the lithosphere that approximately correlates with absolute plate motion (APM) at the time of spreading. We hypothesize that lithosphere formed during ultra-slow seafloor spreading records APM-modified olivine fabric rather than spreading-parallel fabric typical of higher spreading rates. This work highlights the importance of present-day passive margins for improving understanding of the fundamental rift-to-drift transition.},
	keywords = {ambient noise, continental rifting, eastern North American margin, oceanic lithosphere, seismic anisotropy, surface-wave tomography},
	issn = {2169-9356},
	doi = {10.1029/2021JB022955},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2021JB022955},
	author = {Russell, J. B. and Gaherty, J. B.}
}
