HR: 1330h
AN: V42A-0323    [PDF]
TI: Torsion Experiments on Wadsleyite under Transition Zone Conditions
AU: * Xu, Y
EM: yousheng.xu@yale.edu
AF: Yale University, 210 Whiteny Ave, New Haven, CT 06511 United States
AU: Nishihara, Y
EM: yu.nishihara@yale.edu
AF: Yale University, 210 Whiteny Ave, New Haven, CT 06511 United States
AU: Jiang, Z
EM: zhenting.jiang@yale.edu
AF: Yale University, 210 Whiteny Ave, New Haven, CT 06511 United States
AU: Karato, S
EM: shun-ichiro.karato@yale.edu
AF: Yale University, 210 Whiteny Ave, New Haven, CT 06511 United States
AB: Although wadsleyite is the main constituent of the Earth's transition zone, the rheological properties of wadsleyite are poorly constrained because of the difficulty in conducting well-defined deformation experiments under its stability conditions. In order to quantitatively study rheological properties and microstructural development in wadsleyite (and other high-pressure minerals), we are developing a new apparatus for deformation experiments under high-pressure and high-temperature. A rotational actuator is attached to a Drickamer-type opposed anvil apparatus. A thin disk shaped sample is pressurized and heated and then a torque is applied to deform a sample in simple shear. The geometry of deformation is inferred from the geometry of a strain-marker and sample thickness. We find that significant shortening occurs in the initial stage as well as during deformation. Initial stage deformation could influence rheology and microstructural development by introducing dislocations with low-temperature slip systems. To reduce the effects of initial stage deformation, we anneal a sample at a given P and T for ~1 hour. The microstructure of the annealed samples indicates nearly equilibrium grain-boundary morphology suggesting that annealing is nearly complete. Deformation experiments have been made on wadsleyite (as well as for (Mg,Fe)O). The wadsleyite samples were synthesized at 15 GPa and 1273 K for 4 hours and then prepared as discs with diameter of ~1.6 mm and thickness of ~0.2 mm. Deformation experiments on wadsleyite were conducted at ~15 GPa and ~1473 K at a constant rotation rate and the shear strain up to 2 was obtained. Deformation experiments on wadsleyite at higher temperature to large-shear strain, and microstructural observations of samples particularly lattice preferred orientation are being performed. Quantitative rheology measurements will be conducted using the X-ray stress measurements technique at one of the synchrotron beam lines in near future.
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
DE: 8162 Rheology--mantle
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting