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Title: Transition metals in the transition zone: Crystal chemistry of minor element substitution in wadsleyite

Abstract

As the most abundant solid phase at depths of 410 to 525 km, wadsleyite constitutes a large geochemical reservoir in the Earth. In order to better understand the implications of minor element substitution and cation ordering in wadsleyite, we have synthesized wadsleyites coexisting with pyroxenes with about 3 wt% of either TiO 2, Cr 2O 3, V 2O 3, CoO, NiO, or ZnO under hydrous conditions in separate experiments at 1300 °C and 15 GPa. We have refined the crystal structures of these wadsleyites by single-crystal X-ray diffraction, analyzed the compositions by electron microprobe, and estimated M3 vacancy concentration from b/a cell-parameter ratios. According to the crystal structure refinements, trivalent cations Fe 3+, Cr 3+ and V 3+, show a strong preference for M3 over M1 and M2 and significant substitution up to 2.7 % (atomic percent) at the tetrahedral site (T site). Divalent cations, Ni 2+, Co 2+, and Zn 2+ show site preferences similar to those of Fe2+ with M1≈ M3 > M2 > T. Transition metal site preferences appear to correlate with crystal field stabilization energies (CFSE) and are inconsistent with cation radius effects. The avoidance of Ni 2+, Co 2+ and Fe 2+ for the M2more » site in both wadsleyite and olivine can be influenced by CFSE, which has a positive correlation with site preferences at octahedral sites, indicating that avoidance of the lower-symmetry M2 site is stronger for cations having lower (greater absolute value) CFSE. Ti 4+ substitutes primarily into the M3 octahedron, rather than M1, M2, or T sites. Electron microprobe analysis reveals that Ti 4+, Cr 3+, and V 3+ have greater solubility in wadsleyite than in olivine. Furthermore these transition metal cations may be enriched in a melt or an accessory phase if hydrous melting occurs on upward convection across the wadsleyite-olivine boundary and may be useful as indicators of high pressure origin.« less

Authors:
 [1];  [2];  [2];  [3];  [4];  [5]
  1. Univ. of Colorado, Boulder, CO (United States); China Univ. of Geosciences, Wuhan (China)
  2. Univ. of Colorado, Boulder, CO (United States)
  3. Univ. of Bayreuth, Bayreuth (Germany)
  4. Northwestern Univ., Evanston, IL (United States)
  5. China Univ. of Geosciences, Wuhan (China)
Publication Date:
Research Org.:
Carnegie Institution of Washington, Washington, D.C. (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1364627
Grant/Contract Number:  
NA0002006
Resource Type:
Accepted Manuscript
Journal Name:
American Mineralogist
Additional Journal Information:
Journal Volume: 101; Journal Issue: 10; Journal ID: ISSN 0003-004X
Publisher:
Mineralogical Society of America
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; wadsleyite; transition metals; X-ray diffraction; cation ordering

Citation Formats

Zhang, Li, Smyth, Joseph R., Allaz, Julien, Kawazoe, Takaaki, Jacobsen, Steven D., and Jin, Zhenmin. Transition metals in the transition zone: Crystal chemistry of minor element substitution in wadsleyite. United States: N. p., 2016. Web. doi:10.2138/am-2016-5681.
Zhang, Li, Smyth, Joseph R., Allaz, Julien, Kawazoe, Takaaki, Jacobsen, Steven D., & Jin, Zhenmin. Transition metals in the transition zone: Crystal chemistry of minor element substitution in wadsleyite. United States. doi:10.2138/am-2016-5681.
Zhang, Li, Smyth, Joseph R., Allaz, Julien, Kawazoe, Takaaki, Jacobsen, Steven D., and Jin, Zhenmin. Sat . "Transition metals in the transition zone: Crystal chemistry of minor element substitution in wadsleyite". United States. doi:10.2138/am-2016-5681. https://www.osti.gov/servlets/purl/1364627.
@article{osti_1364627,
title = {Transition metals in the transition zone: Crystal chemistry of minor element substitution in wadsleyite},
author = {Zhang, Li and Smyth, Joseph R. and Allaz, Julien and Kawazoe, Takaaki and Jacobsen, Steven D. and Jin, Zhenmin},
abstractNote = {As the most abundant solid phase at depths of 410 to 525 km, wadsleyite constitutes a large geochemical reservoir in the Earth. In order to better understand the implications of minor element substitution and cation ordering in wadsleyite, we have synthesized wadsleyites coexisting with pyroxenes with about 3 wt% of either TiO2, Cr2O3, V2O3, CoO, NiO, or ZnO under hydrous conditions in separate experiments at 1300 °C and 15 GPa. We have refined the crystal structures of these wadsleyites by single-crystal X-ray diffraction, analyzed the compositions by electron microprobe, and estimated M3 vacancy concentration from b/a cell-parameter ratios. According to the crystal structure refinements, trivalent cations Fe3+, Cr3+ and V3+, show a strong preference for M3 over M1 and M2 and significant substitution up to 2.7 % (atomic percent) at the tetrahedral site (T site). Divalent cations, Ni2+, Co2+, and Zn2+ show site preferences similar to those of Fe2+ with M1≈ M3 > M2 > T. Transition metal site preferences appear to correlate with crystal field stabilization energies (CFSE) and are inconsistent with cation radius effects. The avoidance of Ni2+, Co2+ and Fe2+ for the M2 site in both wadsleyite and olivine can be influenced by CFSE, which has a positive correlation with site preferences at octahedral sites, indicating that avoidance of the lower-symmetry M2 site is stronger for cations having lower (greater absolute value) CFSE. Ti4+ substitutes primarily into the M3 octahedron, rather than M1, M2, or T sites. Electron microprobe analysis reveals that Ti4+, Cr3+, and V3+ have greater solubility in wadsleyite than in olivine. Furthermore these transition metal cations may be enriched in a melt or an accessory phase if hydrous melting occurs on upward convection across the wadsleyite-olivine boundary and may be useful as indicators of high pressure origin.},
doi = {10.2138/am-2016-5681},
journal = {American Mineralogist},
number = 10,
volume = 101,
place = {United States},
year = {2016},
month = {10}
}

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