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Phase transition of wadsleyite-ringwoodite in the Mg (sub 2) SiO (sub 4) -Fe (sub 2) SiO (sub 4) system

Noriyoshi Tsujino, Takashi Yoshino, Daisuke Yamazaki, Moe Sakurai, Wei Sun, Fang Xu, Yoshinori Tange and Yuji Higo
Phase transition of wadsleyite-ringwoodite in the Mg (sub 2) SiO (sub 4) -Fe (sub 2) SiO (sub 4) system
American Mineralogist (April 2019) 104 (4): 588-594


The Fe-bearing wadsleyite-ringwoodite phase transition loop under dry conditions in a temperature range of 1473 and 1873 K was determined by in situ X-ray diffraction experiments at the synchrotron facility SPring-8. Pressure at high temperature was precisely determined within a 0.23 GPa error using in situ X-ray diffraction of MgO as a pressure standard. Under dry conditions, assuming an equilibrium chemical composition of wadsleyite and ringwoodite coexisting with garnet in a pyrolite model and an adiabatic temperature gradient with a potential temperature of 1550-1650 K, the phase transition depth and effective width of the seismic discontinuity were found to be 500-514 and 20-22 km, respectively. This effective width, which is three times greater than that of the olivine-wadsleyite phase boundary, can reflect a seismic wave of approximately 0.25 Hz. The wider transition loop between wadsleyite and ringwoodite could create a broad seismic discontinuity. Considering wet and oxidized conditions, the depth of the wadsleyite-ringwoodite phase boundary could be greater than 520 km assuming the small temperature dependency on water and oxygen fugacity effects. Variation in the depth of seismic anomaly may be attributed to water content or oxygen fugacity of the transition zone.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 104
Serial Issue: 4
Title: Phase transition of wadsleyite-ringwoodite in the Mg (sub 2) SiO (sub 4) -Fe (sub 2) SiO (sub 4) system
Affiliation: Okayama University, Institute for Planetary Materials, Tottori, Japan
Pages: 588-594
Published: 201904
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 39
Accession Number: 2019-033990
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Tokyo Institute of Technology, JPN, JapanJapan Synchrotron Radiation Research Institute, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201918
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