HR: 1340h
AN: MR43A-0976    [Abstracts]
TI: Material Yield Strength and Anisotropy in the Nonhydrostatic Diamond Anvil Cell: Implications for Mantle and Core Minerals
AU: * Kavner, A
EM: akavner@ucla.edu
AF: UCLA, Earth & Space Science Dept. 595 Charles Young Drive, East, Los Angeles, CA 90095,
AU: Weinberger, M
EM: mweinberger@ciw.edu
AF: Carnegie Institution of Washington, 5251 Broad Branch Road, Washington, DC 20015,
AB: Hydrostaticity in the diamond anvil cell can be considered as a special case of the generalized three dimensional stress environment in the diamond anvil cell. Recognizing and measuring the extent of non-hydrostaticity can help elucidate measurements of physical properties of mantle and core materials. The amount of differential stress that is supported by a mineral's lattice can be interpreted as a lower-bound on its yield strength, while strength differences among different lattice planes indicate the presence of elastic and/or plastic anisotropy in the sample. Corresponding lattice textural evolution may also help indicate modes of deformation, and may help connect the mineral physics rheology measurements to seismological observations. In addition, measuring the stress environment in the diamond anvil cell is required to make accurate measurements of pressures to interpret phase stability and equation of state data. Here, we present new measurements of yield strength and lattice anisotropy for a materials relevant to the Earth's mantle and core: grossular garnet and Os metal. The differential stress supported by grossular garnet was inferred from synchrotron X-ray measurements of lattice strains in the radial diffraction geometry, and was found to increase from 1.3(±0.6) GPa (at P = 5.8(±1.1) GPa) to 4.1(±0.4) GPa (at P=19(±1.0) GPa ). These results are consistent with inferred strength values for majorite garnet from measurements in the diamond cell normal geometry[1], bolstering the idea that garnet-structured materials may all have similar strengths. However, similar radial diffraction measurements on ringwoodite[2] suggest that this spinel-structured phase is stronger. In fact, the grossular garnet has a similar yield strength as hydrous ringwoodite[3]. This result suggests that the presence of water in the transition zone may not be required to explain a weak rheology, and therefore, models of transition zone behavior built assuming garnet is the high strength phase may need to be revised. The transition metal osmium can be considered as a material analogue for the high pressure behavior of the core mineral, iron. However, the elastic behavior of hexagonal materials has been notoriously difficult to determine using radial diffraction methods. Our measurements of elastic and plastic deformation of Os metal high pressures using in-situ high pressure X-ray diffraction in the radial geometry show that Os has the highest yield strength observed for any pure metal, supporting up to 10 GPa at a pressure of 26 GPa. Furthermore, our data indicate changes in the non-hydrostatic c/a ratio and clear lattice preferred orientation effects at pressures above 15 GPa. We present these results, and examine their implications in light of seismological measurements of inner core anisotropy. References: [1] Kavner, A., S. V. Sinogeikin, J. D. Bass, and R. Jeanloz, "Strength and equation of state of majorite", J. Geophys. Res., 105 pp. 5963-5971, 2000. [2] Kavner, A. and Duffy, T. S., "Strength and elasticity of ringwoodite at upper mantle pressures", Geophys. Res. Lett. 28 p. 2691, 2001 [3] Kavner, A., "Elasticity and strength of hydrous ringwoodite ", Earth Planet. Sci. Lett., 214 pp 645-654. 2003.
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 5120 Plasticity, diffusion, and creep
DE: 8160 Rheology: general (1236, 8032)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting