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Anisotropy

Anisotropy. Shear alignment of olivine crystals. Shear wave splitting. a. c. Olivine Anisotropy: Basic (A-type). [1 0 0] ( a -axis) parallel to flow direction (0 1 0) plane parallel to flow plane Horizontal flow Vsh > Vsv Vertical flow Vsh < Vsv

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Anisotropy

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  1. Anisotropy Shear alignment of olivine crystals

  2. Shear wave splitting a c

  3. Olivine Anisotropy: Basic (A-type) • [1 0 0] (a-axis) parallel to flow direction • (0 1 0) plane parallel to flow plane • Horizontal flow Vsh > Vsv • Vertical flow Vsh < Vsv • Polarization of faster shear wave parallel to flow direction

  4. [0 1 0] Olivine (a-axis projection) [0 0 1]

  5. Olivine (b-axis projection) [0 0 1] [1 0 0]

  6. Olivine (c-axis projection) [0 1 0] A-type: [1 0 0] on (0 1 0) [1 0 0] Vertical Shear

  7. Olivine (c-axis projection) [1 0 0] on (0 1 0) [1 0 0] Horizontal Shear [0 1 0] VSH > VSV A-type

  8. A-type [1 0 0] on (0 1 0)

  9. Olivine anisotropy Vp a c b

  10. Olivine anisotropy Vs a c b

  11. Olivine anisotropy Vs(a-vibration direction is fast) a c b

  12. Olivine anisotropy (Karato et al, 2008) • A-type [1 0 0] on (0 1 0) • B-type [0 0 1] on (0 1 0) • C-type [0 0 1] on (1 0 0) • D-type [1 0 0] on {0 k l} • E-type [1 0 0] on (0 0 1)

  13. Olivine (c-axis projection) [0 1 0] A-type: [1 0 0] on (0 1 0) [1 0 0] Vertical Shear

  14. A-type [1 0 0] on (0 1 0)

  15. [0 1 0] Olivine (a-axis projection) (B-type) [0 0 1] [0 0 1] on (0 1 0)

  16. B-type [0 0 1] on (0 1 0)

  17. Olivine (b-axis projection) (C-type) [1 0 0] [0 0 1]

  18. C-type [0 0 1] on (1 0 0)

  19. [0 1 0] Olivine (a-axis projection) (D-type) [0 0 1] [1 0 0] on (0 k l): Translation is normal to projection plane

  20. D-type [1 0 0] on (0 k l)

  21. Olivine (b-axis projection) (E-type) [0 0 1] [1 0 0]

  22. E-type [1 0 0] on (0 0 1)

  23. Olivine anisotropy Olivine anisotropy

  24. [0 1 0] Olivine (a-axis projection) [0 0 1]

  25. Olivine anisotropy Olivine anisotropy

  26. Olivine anisotropy • Karato group experiments done only up to 2000 H per 106 Si. • Lower asthenosphere conditions allow up to 140,000 H per 106 Si in forsterite. • Explains why Karato sees B- and C-type textures at hydrous conditions. • More data at very hydrous conditions would help.

  27. Olivine anisotropy Expect B-type to predominate if H2O content > 1000 ppm at depth > 200km. 50,000 100,000

  28. Olivine anisotropy • Crystal structure of hydrous forsterite shows vacancies concentrated at M1 with proton on O1-O2 edge. • M1 octahedra form chains parallel to c. • Very hydrous conditions in lower asthenosphere might favor deformations that have offsets along c (B-type and C-type).

  29. [0 1 0] Olivine (a-axis projection) (B-type) [0 0 1]

  30. B-type [0 0 1] on (0 1 0)

  31. Olivine anisotropy • A-type [1 0 0] on (0 1 0) • B-type [0 0 1] on (0 1 0) • C-type [0 0 1] on (1 0 0) • D-type [1 0 0] on {0 k l} • E-type [1 0 0] on (0 0 1) • A, D, and E types align a-axis with shear • B, and C-types align c-axis with shear

  32. Olivine textures

  33. Shear wave splitting a c

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