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Grand challenge program (2002-2007) PIs

Recent Progress in High-Pressure Studies on Plastic Properties of Earth Materials COMPRES meeting at lake Tahoe June, 2004. Grand challenge program (2002-2007) PIs. P. Burnley (Georgia Tech.) H.W. Green (UC Riverside) S. Karato (Yale University) D.J. Weidner (SUNY Stony Brook)

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Grand challenge program (2002-2007) PIs

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  1. Recent Progress in High-Pressure Studies on Plastic Properties of Earth MaterialsCOMPRES meeting at lake TahoeJune, 2004

  2. Grand challenge program (2002-2007)PIs • P. Burnley (Georgia Tech.) • H.W. Green (UC Riverside) • S. Karato (Yale University) • D.J. Weidner (SUNY Stony Brook) • W.B. Durham (LLNL) • [Y. Wang (APS)]

  3. Goal of this project • To develop new techniques of quantitative rheology experiments under deep Earth conditions (exceeding those in the transition zone: ~15 GPa, ~1800 K) • flow laws • deformation microstructures (fabrics)  global dynamics

  4. Quantitative rheological data at high-T from currently available apparatus are limited to P<3 GPa (80 km depth) Rheology of more than 90% of the mantle is unconstrained!

  5. Why high-pressure? • Despite a commonly held view that brittle strength is pressure-sensitive but plastic flow strength is pressure-insensitive, pressure dependence of plastic flow strength is important in Earth’s interior but can be determined only by high-P experiments. • Rheology of high-pressure phases, or rheology associated with a phase transformation (transformational plasticity, transformational faulting) can only be studied under high-P.

  6. Pressure effects Pressure effects are large at high P. [Depends strongly on V* (activation volume). V* in many materials is poorly constrained]

  7. Challenges in high-P rheology studies(How are rheological properties different from elasticity?) • Controlled generation of stress (strain-rate) • Measurements of stress under high-P • Plastic deformation can occur by a variety of mechanisms. • Large extrapolation is needed in time-scale(extrapolation in stress, temperature).  Careful strategy is needed to choose the parameter space and microscopic mechanisms must be identified. • Sensitive to chemical environment and microstructures (large strain is needed to achieve “steady-state” rheology and microstructure).

  8. Pressure effects on creep can be non-monotonic: a simple activation volume formulation may not capture the physics. strength, GPa pressure, GPa

  9. Deformation fabrics (of wadsleyite) depend on conditions of deformation. [MA stress relaxation tests]

  10. Various methods of deformation experiments under high-pressures Rotational Drickamer Apparatus (RDA) Multianvil apparatus stress-relaxation tests DAC D-DIA Very high-P Mostly at room T Unknown strain rate (results are not relevant to most regions of Earth’s interior.) Stress changes with time in one experiment. Complications in interpretation Constant shear strain-rate deformation experiments Large strain possible High-pressure can be achieved. Stress (strain) is heterogeneous. (complications in stress measurements) Constant displacement rate deformation experiments Easy X-ray stress (strain) measurements Strain is limited. Pressure may be limited.

  11. D-DIA (Deformation DIA) High-P and T, homogeneous stress/strain [Pressure exceeding ~15 GPa is difficult. Strain is limited.]

  12. RDA (Rotational Drickamer Apparatus) large strain (radial distribution), high P (because of good support for anvils) [Stress/strain is not uniform. Effects of initial stage deformation must be minimized.]

  13. RDA at X17B2 in NSLS RDA 13 elements SSD Picture Incident X-ray CCD camera Stage

  14. Stress measurement from X-ray diffraction d-spacing becomes orientation-dependent under nonhydrostatic stress. Strain (rate) can also be measured from X-ray imaging.

  15. Lattice strain measured by X-ray is converted to stress using some equations. Equations involve assumptions about stress-strain distribution which is not known apriori. In order to calculate the stress, one needs to understand stress-strain distribution (from the data + modeling). Recent results show significant deviation from elastic model. (Li et al. (2004), Weidener et al. (2004))

  16. 0.005 0.5 GPa 2.0 GPa D0471 (2.510-6) (1.210-5) 6.4 GPa 0.004 D0466 (9.510-6) 1.0 GPa (9.710-6) 0.003 0.002 Lattice strain 0.001 0.5 GPa (1.010-5) 0.000 -0.001 200 220 -0.002 222 -0.003 0 5 10 15 20 25 30 35 Total percent strain MgO: Compression versus extension (D-DIA) 6.4 GPa 1 GPa 1000K Strain rate: 0.9x10-5 s-1 Uchida et al. 2004, submitted

  17. Plastic deformation of olivine (Li et al., 2004)

  18. stress-distribution in a RDA

  19. Sample and diffraction geometry ~0.4 mm ring width Observed part by diffraction Diffracted X-ray (50 mm wide) Incident X-ray (50 mm wide) 6.5º 0.9 mm Effective length for diffraction

  20. Stress-strain conditions in sample 1 Z Y s1 Y s3 s1 s3 Simple shear Uniaxial compression Principal stress (s1, s3) direction Y = 0 and 90º Y = +45 and -45º Variation of d-spacing (Assuming . elastically isotropic) Hydrostatic d0: d for hydrostatic condition G: shear modulus t: Uniaxial deviatoric stress sS: Shear deviatoric stress

  21. 27ºC During rotation at P=15 GPa and T=1600 K Annealing at P=15 GPa after compression t = 0.6 GPa, sS = 0.7 GPa 300 K 900 K 1600 K By using Y = 0, ±45, ±90º geometry, uniaxial deviatoric stress and simple shear deviatoric stress can be determined independently.

  22. Pressure dependence of olivine rheology Li et al. (2004), V*< 3 cc/mol Karato and Jung. (2003) Karato (1977), V*=13.9 cc/mol (theory) Ross et al. (1979), V*~13 cc/mol Green and Borch (1987), V*~27 cc/mol Bussod et al. (1993), V*~5-10 cc/mol Karato and Rubie (1997), V*~14 cc/mol Karato and Jung. (2003), V*~14, 24 cc/mol Li et al. (2004), V*< 3 cc/mol

  23. Summary • Two new apparati have been developed (D-DIA and RDA). • Quantitative high-P and T deformation experiments have been conducted to ~10 GPa (MgO, olivine) by D-DIA and ~15 GPa by RDA (hcp-Fe, olivine, (Mg,Fe)O, wadsleyite, ringwoodite). --------------------------------------------------------- • Significant discrepancy exists between some of the high-P results and lower-P (better constrained) data (V*): parameterization problem? • Maximum P with D-DIA is ~10 GPa. • How to get higher P? harder anvil materials (sintered diamond?)

  24. Summary (cont.) • Deformation geometry with RDA is less than ideal. • Larger uncertainties in mechanical data. • Theoretical problems with stress measurements by X-ray diffraction sample assembly, better alignment • Chemical environment is not well controlled. stress/strain distribution in deforming polycrystals (heterogeous materials)

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