NAL phase in K-rich portions of the lower mantle

作者：Kato Chie^*; Hirose Kei; Komabayashi Tetsuya; Ozawa Haruka; Ohishi Yasuo

来源：Geophysical Research Letters, 2013, 40(19): 5085-5088.

DOI：10.1002/grl.50966

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

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.

• 出版日期2013-10-16