Olivine-wadsleyite transition in the system (Mg,Fe )2SiO4

Tomoo Katsura, Hitoshi Yamada, Osamu Nishikawa, Maoshuang Song, Atsushi Kubo, Toru Shinmei, Sho Yokoshi, Yoshitaka Aizawa, Takashi Yoshino, Michael J. Walter, Eiji Ito, Ken Ichi Funakoshi

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Abstract

Phase relations of the olivine-wadsleyite transition in the system (Mg,Fe)2SiO4 have been determined at 1600 and 1900 K using the quench method in a Kawai-type high-pressure apparatus. Pressure was determined at a precision better than 0.2 GPa using in situ X-ray diffraction with MgO as a pressure standard. The transition pressures of the end-member Mg2SiO4 are estimated to be 14.2 and 15.4 GPa at 1600 and 1900 K, respectively. Partition coefficients for Fe and Mg between olivine and wadsleyite are 0.51 at 1600 K and 0.61 at 1900 K. By comparing the depth of the discontinuity with the transition pressure, the temperature at 410 km depth is estimated to be 1760 ± 45 K for a pyrolitic upper mantle. The mantle potential temperature is estimated to be in the range 1550-1650 K. The temperature at the bottom of the upper mantle is estimated to be 1880 ± 50 K. The thickness of the olivine-wadsleyite transition in a pyrolitic mantle is determined to be between 7 and 13 km for a pyrolitic mantle, depending on the efficiency of vertical heat transfer. Regions of rapid vertical flow (e.g., convection limbs), in which thermal diffusion is negligible, should have a larger transition interval than stagnant regions, where thermal diffusion is effective. This is in apparent contradiction to short-period seismic wave observations that indicate a maximum thickness of <5 km. An upper mantle in the region of the 410 km discontinuity with about 40% olivine and an Mg# of at least 89 can possibly explain both the transition thickness and velocity perturbation at the 410 km discontinuity.

Original languageEnglish
Pages (from-to)B02209 1-12
JournalJournal of Geophysical Research: Solid Earth
Volume109
Issue number2
Publication statusPublished - Feb 10 2004

Keywords

  • 410 km discontinuity
  • Composition of the mantle
  • Mantle geotherm
  • Olivine-wadsleyite transition
  • Phase relations

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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    Katsura, T., Yamada, H., Nishikawa, O., Song, M., Kubo, A., Shinmei, T., Yokoshi, S., Aizawa, Y., Yoshino, T., Walter, M. J., Ito, E., & Funakoshi, K. I. (2004). Olivine-wadsleyite transition in the system (Mg,Fe )2SiO4. Journal of Geophysical Research: Solid Earth, 109(2), B02209 1-12.