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The Impact of the Deformation History on the Microstructural Evolution of Polycrystalline Olivine and How It Affects the Interpretation of Mantle Seismic Anisotropy
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  • Albert Griera,
  • Enrique Gomez-Rivas,
  • Ricardo Lebensohn,
  • Maria-Gema Llorens
Albert Griera
Universitat Autònoma de Barcelona

Corresponding Author:[email protected]

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Enrique Gomez-Rivas
Universitat de Barcelona
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Ricardo Lebensohn
Los Alamos National Laboratory
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Maria-Gema Llorens
Universitat Autònoma de Barcelona
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Relating seismic anisotropy with mantle flow requires a good understanding of the rock’s microstructural evolution and the development of crystal preferred orientations (CPO), because plastic deformation of olivine is interpreted as the main cause for mantle seismic anisotropy. In this contribution, the influence of deformation history in the microstructure evolution and resulting seismic anisotropy is investigated by means of full-field numerical simulations at the microscale. We explicitly simulate the microstructural evolution of olivine polycrystalline aggregates during dynamic recrystallization up to high strain using the code VPFFT/ELLE (e.g. Griera et al., 2011; 2013; Llorens et al., 2016). Modeling results indicate that the evolution of a CPO is highly sensitive to the initial olivine fabric. When the initial fabric is formed by a random distribution of crystallographic orientations, there is a rapid alignment of the a-axes (or [100]) with the stretching direction of flow. However, when there is an initial CPO inherited from previous deformation, larger strains are required for the a-axes to become re-aligned with the stretching direction. Our numerical results agree with field and experimental observations (e.g. Boneh and Skemer, 2014; Skemer et al., 2012). The analysis of the seismic properties reveals that an increase of the strength of the initial inherited CPO produces a reduction of the azimuthal seismic anisotropy, compared to the case with an initial random fabric. It is concluded that the deformation history significantly influences the development of fabrics. Accordingly, seismic anisotropy interpretations must be carried out with caution in regions with complex deformation histories. References Boneh Y., Skemer P. 2014. EPSL, 406. Griera A, et al. 2011. Geology 39, 275-278. Griera A, et al. 2013. Tectonophysics 587, 4-29. Llorens, M.-G. et al. 2016 EPSL, 450, 233-242. Skemer P. et al. 2012. Geochemistry Geophysics Geosystems, 13:3.