Premium
Elasticity of hydrous wadsleyite to 12 GPa: Implications for Earth's transition zone
Author(s) -
Mao Z.,
Jacobsen S. D.,
Jiang F.,
Smyth J. R.,
Holl C. M.,
Duffy T. S.
Publication year - 2008
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 - 10.1029/2008gl035618
Subject(s) - transition zone , ringwoodite , mantle (geology) , geology , bulk modulus , mineralogy , olivine , shear modulus , s wave , elasticity (physics) , geophysics , materials science , composite material
Knowledge of the pressure effect on elasticity of hydrous olivine polymorphs is necessary to model seismic wave speeds for potential hydrous regions of the mantle. Here we report single‐crystal elastic properties of wadsleyite, β ‐Mg 2 SiO 4 , with 0.84 wt.% H 2 O measured to 12 GPa by Brillouin scattering. Pressure derivatives of the aggregate bulk modulus, K ′ S 0 , and shear modulus, G ′ 0 , of hydrous wadsleyite are 4.1(1) and 1.4(1) respectively. These values are indistinguishable within uncertainty from those of anhydrous wadsleyite. We estimate that ∼1 wt.% H 2 O in wadsleyite at 410‐km depth can reconcile seismic bulk sound velocities with a pyrolite‐composition mantle by using our measured high‐pressure elastic constants. If the H 2 O content of the mantle is much less than 1 wt.%, then other factors need to be considered to explain the velocity contrast of the 410‐km discontinuity. Variations in water content with depth may also contribute to the anomalously steep seismic velocity gradient in the mantle transition zone.