NAL phase in K-rich portions of the lower mantle

The stability of the K‐rich new aluminous (NAL) phase was examined on the join Na1.00Mg2.00Al4.80Si1.15O12‐K1.00Mg2.00Al4.80Si1.15O12 (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,...

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Bibliographic Details
Published in:Geophysical research letters 2013-10, Vol.40 (19), p.5085-5088
Main Authors: Kato, Chie, Hirose, Kei, Komabayashi, Tetsuya, Ozawa, Haruka, Ohishi, Yasuo
Format: Article
Language:English
Subjects:
Al phase
Anisotropy
CF phase
high pressure
lower mantle
NAL phase
phase relation
Phase transitions
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Summary:The stability of the K‐rich new aluminous (NAL) phase was examined on the join Na1.00Mg2.00Al4.80Si1.15O12‐K1.00Mg2.00Al4.80Si1.15O12 (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
ISSN:0094-8276
1944-8007
DOI:10.1002/grl.50966