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Energetics, equation of state, and elasticity of NAL phase: Potential host for alkali and aluminum in the lower mantle
Author(s) -
Mookherjee Mainak,
Karki Bijay B.,
Stixrude Lars,
LithgowBertelloni Carolina
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl053682
Subject(s) - mantle (geology) , subduction , alkali metal , thermodynamics , elasticity (physics) , equation of state , mineralogy , geology , materials science , phase (matter) , analytical chemistry (journal) , chemistry , geochemistry , physics , tectonics , organic chemistry , chromatography , paleontology
The new aluminous (NAL) phase and aluminous phase with calcium ferrite (CF) structure constitutes more than 25 volume % of the deeply subducted crust at lower mantle depths. Using first principle simulations, we calculate the energetics, equation of state, and elasticity of NAL phase with a widely varying composition including CaMg 2 Al 6 O 12 , NaNa 2 Al 3 Si 3 O 12 and KNa 2 Al 3 Si 3 O 12 . Our calculations indicate the relative stability of NAL and CF phases is a sensitive function of pressure, temperature, and composition, with increasing pressure tending to favor the CF phase, and increasing temperature, Mg‐content and alkali‐content tending to favor the NAL phase. The sound wave velocities of the NAL phase is significantly lower than CF phases and other major lower mantle phases. In deeply subducted MORB and CC, the faster sound velocity of silica (SiO 2 ) and its high‐pressure polymorphic phase is likely to be compensated with the slower sound wave velocities of NAL phase.