NAL phase in K-rich portions of the lower mantle

Chie Kato, Kei Hirose, Tetsuya Komabayashi, Haruka Ozawa, Yasuo Ohishi

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The stability of the K-rich new aluminous (NAL) phase was examined on the join Na1.00Mg2.00Al4.80Si1.15O 12-K1.00Mg2.00Al4.80Si 1.15O12 (Na100-K100) up to 144 GPa by X-ray diffraction in a laser-heated diamond anvil cell. Single-phase K100 and Na50K50 NAL were formed up to the lower mantle conditions, and the NAL phase coexisted with the calcium ferrite-type (CF) phase at 120 GPa and 2300 K for the Na75K25 bulk composition. This is a striking contrast to the K-free (Na100) NAL that becomes unstable above 27 GPa at 1850 K, which suggests that potassium stabilizes NAL at significantly higher pressures. K-rich NAL may host potassium in the lower mantle that contains K2O more than 0.09 wt %. In addition, the NAL phase likely formed owing to partial melting in the ultralow-velocity zone or because of a basal magma ocean. Future seismological observations may clarify whether NAL is a radiogenic heat source above the core-mantle boundary. Key Points Potassium expands the stability of the NAL phase dramatically K-rich NAL is stable o the lowermost mantle conditions NAL forms in the whole lower mantle where the K2O content is higher than 900 ppm

Original languageEnglish
Pages (from-to)5085-5088
Number of pages4
JournalGeophysical Research Letters
Issue number19
Publication statusPublished - Oct 16 2013


  • Al phase
  • CF phase
  • NAL phase
  • high pressure
  • lower mantle
  • phase relation

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)

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  • Cite this

    Kato, C., Hirose, K., Komabayashi, T., Ozawa, H., & Ohishi, Y. (2013). NAL phase in K-rich portions of the lower mantle. Geophysical Research Letters, 40(19), 5085-5088.