Transition metals in the transition zone: partitioning of Ni, Co, and Zn between olivine, wadsleyite, ringwoodite, and clinoenstatite

Li Zhang*, Joseph R. Smyth, Takaaki Kawazoe, Steven D. Jacobsen, Shan Qin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Ni, Co, and Zn are widely distributed in the Earth’s mantle as significant minor elements that may offer insights into the chemistry of melting in the mantle. To better understand the distribution of Ni2+, Co2+, and Zn2+ in the most abundant silicate phases in the transition zone and the upper mantle, we have analyzed the crystal chemistry of wadsleyite (Mg2SiO4), ringwoodite (Mg2SiO4), forsterite (Mg2SiO4), and clinoenstatite (Mg2Si2O6) synthesized at 12–20 GPa and 1200–1400 °C with 1.5–3 wt% of either NiO, CoO, or ZnO in starting materials. Single-crystal X-ray diffraction analyses demonstrate that significant amounts of Ni, Co, and Zn are incorporated in octahedral sites in wadsleyite (up to 7.1 at%), ringwoodite (up to 11.3 at%), olivine (up to 2.0 at%), and clinoenstatite (up to 3.2 at%). Crystal structure refinements indicate that crystal field stabilization energy (CFSE) controls both cation ordering and transition metal partitioning in coexisting minerals. According to electron microprobe analyses, Ni and Co partition preferentially into forsterite and wadsleyite relative to coexisting clinoenstatite. Ni strongly prefers ringwoodite over coexisting wadsleyite with DNiRw/Wd = 4.13. Due to decreasing metal–oxygen distances with rising pressure, crystal field effect on distribution of divalent metal ions in magnesium silicates is more critical in the transition zone relative to the upper mantle. Analyses of Ni partitioning between the major upper-mantle phases implies that Ni-rich olivine in ultramafic rocks can be indicative of near-primary magmas.

Original languageEnglish (US)
Article number52
JournalContributions to Mineralogy and Petrology
Volume173
Issue number7
DOIs
StatePublished - Jul 1 2018

Funding

This study was supported by US National Science Foundation Grant EAR 11-13369 and EAR 14-16979 to JRS. SDJ acknowledges support from US National Science Foundation Grant EAR-1452344, the Carnegie/DOE Alliance Center, the David and Lucile Packard Foundation, and the Alexander von Humboldt Foundation. Multi-anvil experiments were supported by Bayerisches Geoinstitut Visitors Program.

Keywords

  • Cation ordering
  • Element distribution
  • Transition zone
  • X-ray diffraction

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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