@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 {dunn_crustal_2013,
	title = {Crustal construction and magma chamber properties along the Eastern Lau Spreading Center},
	journal = {Earth and Planetary Science Letters},
	volume = {371-372},
	year = {2013},
	month = {jun},
	pages = {112{\textendash}124},
	abstract = {The L-SCAN active-source seismic tomography experiment maps the crustal structure and magmatic system along a 120-km-long section of the back-arc Eastern Lau Spreading Center (ELSC), where the ridge undergoes abrupt changes in morphology and composition associated with increasing proximity to the Tofua volcanic arc. Using this dataset, we picked \textasciitilde197,000 P-wave travel times from 57 seismic airgun lines recorded at 83 ocean bottom seismograph stations, and inverted for a 3-D P-wave velocity image. The seismic images reveal a prominent, but narrow, seismic low velocity volume (LVV) located beneath all surveyed ridge segments, consistent with the high temperatures and melt of a crustal magmatic system. Crustal magmatic systems thus underlie spreading axes even where previous seismic reflection surveys did not detect magma lens reflectors, accounting for the heat source of high-temperature hydrothermal vents in these areas. The top of the LVV closely follows the ridge axis and steps across three overlapping spreading centers. As the offset of the overlap increases, the LVV becomes increasingly discontinuous across the ridge limbs. Surprisingly, the LVV is as much as twice as wide, but deeper, in the northern part of the ridge system where the crust is thinner, as compared to the LVV beneath the southern segments, where the crust is relatively thicker. The width of the LVV may be modulated by the degree of deep hydrothermal activity or temporal variations in melt supply, and thus may not correlate directly with the average melt flux as indicated by crustal thickness. Over the past 4Myr, the location of the ridge has swept across different mantle compositional domains, and the crust produced at the ridge formed a zoned pattern. The interpretation is that thick, highly porous, volcanic layers with felsic compositions cap regions of thick crust; thinner volcanic layers of basaltic composition cap regions of thinner crust. The zonal pattern indicates that the influence of slab-derived water on crustal construction has substantially decreased over time.},
	keywords = {back-arc basin, Eastern Lau Spreading Center, magma chamber, mantle melting, mid-ocean ridge, seismic tomography},
	issn = {0012-821X},
	doi = {10.1016/j.epsl.2013.04.008},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X13001891},
	author = {Dunn, Robert A. and Martinez, Fernando and Conder, James A.}
}
@article {holmes_crustal_2008,
	title = {Crustal thickness variations along the Southeast Indian Ridge (100{\textdegree}{\textendash}116{\textdegree}E) from 2-D body wave tomography},
	journal = {Geochemistry, Geophysics, Geosystems},
	volume = {9},
	number = {12},
	year = {2008},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2008GC002152},
	abstract = {Axial morphology along the Southeast Indian Ridge (SEIR) systematically changes from an axial high to a deep rift valley at a nearly uniform intermediate spreading rate between 100{\textdegree}{\textendash}116{\textdegree}E, west of the Australian-Antarctic Discordance (AAD). Basalt geochemistry has a consistent Indian{\textendash}mid-ocean ridge basalt (MORB) type isotopic signature, so changes in axial topography are attributed to variations in both mantle temperature and melt supply. Wide-angle seismic refraction lines were shot to four ocean bottom hydrophones within SEIR segments P1, P2, S1, and T, where each segment is characterized by a different morphology. We constructed 2-D crustal velocity models by jointly inverting hand-picked P wave refraction (Pg) and Moho reflection (PmP) traveltime data using a top-down, minimum-structure methodology. The results show a 1.5 km eastward decrease in crustal thickness across the study area, with segment averages ranging from 6.1 km at P1 to 4.6 km at T. Melt generation models require a \~{}30{\textdegree}C decrease in mantle temperature toward the AAD to account for the crustal thickness trend. Significant changes in axial morphology accompany small-scale variations in crustal thickness, consistent with models of crustal accretion where ridge topography is determined by a balance between mantle temperature, melt supply, and cooling from hydrothermal circulation. Layer 3 thins by 3.0 km as layer 2 thickens by 1.4 km between segments P1 and T, reflecting the eastward decrease in melt supply and increase in melt lens depth. The trade-off in seismic layers may be explained by models relating the increase in overburden pressure on a deepening melt lens to the volume of magma erupted into the upper crust rather than cooling at depth to form new lower crustal material.},
	keywords = {crustal structure, mid-ocean ridge, oceanic crust, seismic refraction, seismic tomography, Southeast Indian Ridge},
	issn = {1525-2027},
	doi = {10.1029/2008GC002152},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2008GC002152},
	author = {Holmes, R. Chadwick and Tolstoy, Maya and Cochran, James R. and Floyd, Jacqueline S.}
}
