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Thermal elasticity of (Fe x ,Mg 1− x ) 2 SiO 4 olivine and wadsleyite
Author(s) -
NúñezValdez M.,
Wu Z.,
Yu Y. G.,
Wentzcovitch R. M.
Publication year - 2013
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 - 10.1002/grl.50131
Subject(s) - olivine , forsterite , transition zone , mantle (geology) , geology , shear (geology) , mineralogy , shear modulus , classification of discontinuities , bulk modulus , ringwoodite , peridotite , shear velocity , materials science , discontinuity (linguistics) , thermodynamics , geophysics , petrology , composite material , physics , turbulence , mathematical analysis , mathematics
We present first‐principles results for elastic moduli (bulk, K , and shear, G ) and acoustic velocities (compressional, V P , shear, V S , and bulk V Φ ) of olivine ( α ) and wadsleyite ( β ) (Fe x ,Mg 1 − x ) 2 SiO 4 , at high pressure ( P ) and temperature ( T ) with varying iron content (0 ≤ x ≤ 0.125). Pressure and temperature derivatives of these properties are analyzed. We show that adding 12.5% of Fe in forsterite softens V P and V S by ∼3–6%, the same effect as raising temperature by ∼1000 K in dry olivine at 13.5 GPa—the same is true in wadsleyite. This study suggests that Fe is effective in producing seismic velocity heterogeneity at upper mantle and transition zone conditions and should be another key ingredient, in addition to temperature and water content variations, in interpreting seismic heterogeneities in the transition zone. The effect of Fe on density, elastic, and velocity contrasts across the α → β transition is also addressed at relevant conditions. We show that simultaneous changes of composition, temperature, and pressure do not affect significantly the relative density contrasts. We also find that compressional and shear impedance contrasts result primarily from velocity discontinuities rather than density discontinuity.