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Viscous anisotropy and its role in maintaining lithospheric -scale transform faults

Viscous anisotropy and its role in maintaining lithospheric -scale transform faults. Lars N. Hansen (Stanford) Jessica Warren (Stanford) Mark E. Zimmerman (U. Minnesota) David L. Kohlstedt (U. Minnesota). 28. Anisotropy and localization of deformation. [100]. [010]. [001].

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Viscous anisotropy and its role in maintaining lithospheric -scale transform faults

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  1. Viscous anisotropy and its role in maintaining lithospheric-scale transform faults Lars N. Hansen (Stanford) Jessica Warren (Stanford) Mark E. Zimmerman (U. Minnesota) David L. Kohlstedt (U. Minnesota) 28

  2. Anisotropy and localization of deformation [100] [010] [001] Tommasi et al., Nat. Geosci., 2009

  3. Measuring anisotropy in the lab

  4. How long do the rocks remember? 5 mm 5 mm tension torsion

  5. Angle of [100] to shear direction (°) Ni jacket 0 90 500 µm Center of sample Multiples of uniform density edge center

  6. [1 0 0] [0 1 0] [0 0 1] shear direction

  7. How long do the rocks remember? crust mantle Strain after ~10 km offset ~0.5 Myr Bonninet al.,Geophys. J. Inter., 2012

  8. How long do the rocks remember? crust mantle Strain after ~10 km offset ~0.5 Myr Any new boundary conditions need to be sustained at least this long! Bonninet al.,Geophys. J. Inter., 2012

  9. fin

  10. How much weakening from CPO vs. grain size? Predicted stress based on change in grain size About 30% reduction in stress from CPO

  11. Sample jacketed in iron

  12. initially anisotropic initially isotropic

  13. initially anisotropic initially isotropic

  14. Mantle rocks significantly affect fault reorientation if rotation rate of forces > rotation rate of fabric

  15. Anisotropy will impact new boundary conditions if rotation rate of forces > rotation rate of fabric crust mantle Strain after ~10 km offset ~0.5 Myr Bonninet al.,Geophys. J. Inter., 2012

  16. Anisotropy will impact new boundary conditions if rotation rate of forces > rotation rate of fabric crust mantle Strain after ~10 km offset ~0.5 Myr Bonninet al.,Geophys. J. Inter., 2012 critical rate ≈ 5 to 30°/Myr

  17. σ = 1 MPa dry olivine dislocation creep

  18. How long do the rocks remember?

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