HR: 16:00h
AN: MR24A-01 INVITED     [Abstracts]
TI: Development of a rotational Drickmaer apparatus for large-strain deformation experiments under deep Earth conditions
AU: * Nishihara, Y
EM: yu.nishihara@yale.edu
AF: Yale University, Department of Geology and Geophysics, New Haven, CT 06520 United States
AU: Xu, Y
EM: yousheng.xu@yale.edu
AF: Yale University, Department of Geology and Geophysics, New Haven, CT 06520 United States
AU: Karato, S
EM: shun-ichiro.karato@yale.edu
AF: Yale University, Department of Geology and Geophysics, New Haven, CT 06520 United States
AB: Developing an apparatus for quantitative deformation experiments beyond the transition zone pressures ($>$15 GPa) is critical for understanding whole mantle geodynamics. A new type of torsion apparatus "Rotational Drickamer Apparatus (RDA)" has been developed in which large-strain deformation experiments have been performed at pressures and temperatures up to $\sim$15 GPa and $\sim$1700 K respectively. The apparatus consists of opposing anvils made of tungsten carbide that are supported by a pyrophyllite gasket. A sample is located between two anvils sandwiched between alumina or YAG disks. The sample space is heated by two disk heaters made of a mixture of TiC and diamond. Deformation is achieved by rotating one anvil relative to another through a Harmonic Drive $^{TM}$ gear box. Deformation experiments up to $\sim$15 GPa and $\sim$1700 K to shear strains of up to $\sim$2 have been performed for samples of (Mg,Fe)O and (Mg,Fe) $_{2}$SiO $_{4}$ olivine and wadsleyite at the rotation rates of 3-7 x 10$^{-4}$ rpm corresponding to the shear strain rates of 0-5 x 10$^{-4}$ s$^{-1}$. A conical window is made in a cylinder containing the anvils for the X-ray {\it in-situ} stress and strain measurements. In this apparatus, both uniaxial compression and shear deformation occur. To determine uniaxial stress and shear stress separately, X-ray diffraction measurements were performed at five different angles with respect to the rotation (compression) axis (i.e., $0\deg$, $\pm$$45\deg$, $\pm$$90\deg$). The sample thickness change and shear deformation were monitored by an imaging system in the synchrotron experiments. This apparatus allows quantitative studies of plastic deformation and deformation microstructural development at a fixed strain-rate under the pressure and temperature conditions equivalent to deep mantle exceeding $\sim$500 km depth.
DE: 3630 Experimental mineralogy and petrology
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting