Rachel Eleanor Bernard

I collect and study xenoliths, rocks that come up from lower crust and upper mantle depths through volcanic eruptions

My research broadly aims to understand deformation in the lithosphere. I have focused on the rheological properties of the lower crust and upper mantle, particularly in actively deforming regions such as the Mojave region of Southern California (Bernard and Behr, 2017, JGR Solid Earth) or Baja California (Bernard et al., 2023, LITHOS). I've also worked to understand the factors that influence the development of olivine and pyroxene crystallographic preferred orientation (CPO), a result of dislocation creep that is primarily responsible for seismic anisotropy in the upper mantle (Bernard et al., 2019, G-cubed; Bernard et al. 2021, Tectonophysics).

Ott, J. N., Condit, C. B., Schulte-Pelkum, V., Bernard, R., & Pec, M. (2024). Seismic anisotropy of mafic blueschists: EBSD-based constraints from the exhumed rock record. Journal of Geophysical Research: Solid Earth, 129, e2023JB027679. https://doi.org/10.1029/2023JB027679

Bernard, R. E., Chin, E. J., Murphy, C. (2023) Melt-assisted deformation in the lower crust of an active plate boundary, Baja California. LITHOS. DOI: 10.1016/j.lithos.2022.106975

Bernard R.E., Schulte-Pelkum, V., and W.M. Behr (2021) The competing effects of olivine and orthopyroxene CPO on seismic anisotropy. Tectonophysics. DOI: 10.1016/j.tecto.2021.228954

Bernard, R.E., Behr, W.M., Becker, T.W., and D.J. Young (2019) Relationships between olivine CPO and deformation parameters in naturally deformed rocks and implications for mantle seismic anisotropy. Geochemistry, Geophysics, Geosystems. DOI: 10.1029/2019GC008289

Bernard, R.E. and W.M Behr (2017) Fabric heterogeneity in the Mojave lower crust and lithospheric mantle in Southern California. JGR Solid Earth. DOI: 10.1002/2017JB014280

Among all of the various analytical techniques I employ in my research, electron backscatter diffraction (EBSD) is my favorite. This powerful technique allows for the identification of mineral phases based on their crystallographic structure, while also quantifying the orientations of those minerals. We can express these measurements in stereographic projections or pole figures, or make beautiful maps like the ones shown above. (top) EBSD phase map of an awesome, highly deformed peridotite xenolith from Lunar Crater Volcanic Field in central Nevada; (bottom) the same mapped area, but with olivine colored based on orientation. This type of map allows us to investigate grain elongation, dynamic recrystallization, and CPO preserved in this spectacularly deformed rock.