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

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