Title: Complexities of olivine crystallographic preferred orientation and implications for mantle seismic anisotropy
Speaker: Dr. Rachel Bernard
Visiting Assistant Professor of Geology and Postdoctoral Fellow, Amherst College.
Lead author of "No progress on diversity in 40 years" in Nature Geoscience in 2018.
Abstract: Olivine crystallographic preferred orientation (CPO) forms through viscous deformation and is the primary cause of upper mantle seismic anisotropy. Laboratory experiments suggest that deformation conditions (specifically water content, stress magnitude, pressure and temperature) play key roles in the development of olivine CPO “types,” which themselves directly influence how we infer mantle flow directions from observations of seismic anisotropy. This talk highlights results of a study utilizing 65 peridotites from a wide range of tectonic settings to investigate whether naturally deformed samples agree with these experiments. The samples investigated here were also combined with an extensive literature review of over 500 published samples from 52 localities, and reveal that water content, stress magnitude, pressure, and temperature may affect olivine CPO development less in nature than deformation history and geometry. The complex relationships found between olivine CPO and deformation conditions may explain the lack
of agreement between geophysical models and seismic anisotropy patterns in the continental mantle lithosphere. This study highlights the difficulty in using olivine CPO in natural peridotites to infer deformation conditions and the need for more rock deformation experiments.
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