DI030-07
Anisotropy of the Upper Mantle Transition Zone constrained from the first experimentally determined high temperature-pressure single-crystal elasticity data of wadsleyite

Wednesday, 16 December 2020: 05:55
Virtual
Wenyi Zhou1, Ming Hao1, Tomohiro Ohuchi2, Bin Chen3, Lowell M Miyagi4, Brandon Schmandt5 and Jin Zhang1, (1)University of New Mexico, Institute of Meteoritics, Department of Earth and Planetary Sciences, Albuquerque, NM, United States, (2)Ehime University, Geodynamics Research Center, Matsuyama, Japan, (3)University of Hawaii at Manoa, Hawaii Institute of Geophysics and Planetology, Honolulu, HI, United States, (4)University of Utah, Department of Geology and Geophysics, Salt Lake City, UT, United States, (5)University of New Mexico, Department of Earth & Planetary Sciences, Albuquerque, NM, United States
Recorded Presentation
Abstract:
Recent global seismic observations suggested the presence of anisotropy in the Upper Mantle Transition Zone (UMTZ, 410-520 km), especially near some subduction zones (e.g., beneath the Tonga slab)1,2. Wadsleyite is the main anisotropic contributor to the UMTZ due to the elastically isotropic properties of garnet and the small volume proportion of pyroxene (<10 vol%)3. Understanding the seismic anisotropy in the UMTZ requires the knowledge of the deformation fabrics as well as the single-crystal elastic properties (Cijs) of wadsleyite. Although the fabrics of wadsleyite has been well-studied4, no experiment has been conducted to constrain the high temperature-pressure Cijs of wadsleyite thus far. In this study, we carried out single-crystal Brillouin spectroscopy experiments for the wadsleyite sample (Mg0.906Fe0.094)1.9885H0.023SiO4 (0.14 (5) wt% water) up to 16.6 GPa 700 K. We found that C11, C22, and, C33 are more sensitive to temperature compared with other Cijs, in particular, C12 is least sensitive to temperature. Based on our obtained pressure-temperature dependent Cijs, and the deformation experimental results from Ohuchi et al (2014)4, we modeled the seismic anisotropy generated by dislocation creep of wadsleyite aggregates and interpreted the UMTZ seismic anisotropy observed globally and locally in subduction zone regions.

References: [1] Visser, K., Trampert, J., Lebedev, S. and Kennett, B.L.N., 2008. Probability of radial anisotropy in the deep mantle. Earth and Planetary Science Letters, 270(3-4), pp.241-250. [2] Foley, B.J. and Long, M.D., 2011. Upper and mid‐mantle anisotropy beneath the Tonga slab. Geophysical Research Letters, 38(2). [3] Frost, D.J., 2008. The upper mantle and transition zone. Elements, 4(3), pp.171-176. [4] Ohuchi, T., Fujino, K., Kawazoe, T. and Irifune, T., 2014. Crystallographic preferred orientation of wadsleyite and ringwoodite: Effects of phase transformation and water on seismic anisotropy in the mantle transition zone. Earth and Planetary Science Letters, 397, pp.133-144.

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