Elasticity of Ferro-Periclase Through
the High Spin - Low Spin Transition
J. Michael Brown - University of WashingtonJonathan Crowhurst - Lawrence Livernmore Lab.
Alexander Goncharov - Geophysical Lab.Steven Jacobsen - Northwestern University
J. Michael Brown - University of WashingtonJonathan Crowhurst - Lawrence Livernmore Lab.
Alexander Goncharov - Geophysical Lab.Steven Jacobsen - Northwestern University
Summary(Three Major Topics)
Summary(Three Major Topics)
Mantle Tomography: Why are slabs hard to image in the lower mantle? Do not penetrate? Off-setting chemical and thermal effects?
High spin - low spin transition?
Mantle Tomography: Why are slabs hard to image in the lower mantle? Do not penetrate? Off-setting chemical and thermal effects?
High spin - low spin transition?
Summary(Three Major Topics)
Summary(Three Major Topics)
Mantle Tomography: Why are slabs hard to image in the lower mantle? Do not penetrate? Off-setting chemical and thermal effects?
High spin - low spin transition?
Mantle Tomography: Why are slabs hard to image in the lower mantle? Do not penetrate? Off-setting chemical and thermal effects?
High spin - low spin transition?
Physics of the High spin low spin transition Outstanding experimental data Robust macroscopic thermodynamic theory
Physics of the High spin low spin transition Outstanding experimental data Robust macroscopic thermodynamic theory
New measurements of sound velocities through the HS-LS transition Some experimental details All elastic constants determined to 63 GPa
Help validate the macroscopic thermodynamic description
Support idea that thermal anomalies have small velocity perturbations in lower mantle
New measurements of sound velocities through the HS-LS transition Some experimental details All elastic constants determined to 63 GPa
Help validate the macroscopic thermodynamic description
Support idea that thermal anomalies have small velocity perturbations in lower mantle
Less structure in lower mantle
Less structure in lower mantle
A possible connection to the high-spin low-spin transition
“Using the best mineral physics data, slabs should be visible in seismic images of the mid lower mantle - that they are not seen is somewhat surprising” Guy Masters 2006 AGU meeting
Physics of the High spin to Low spin
Transition
Physics of the High spin to Low spin
Transition
High spin - low spin iron
High spin - low spin iron
Transition is Intrinsically non-1st order Readily described by robust macroscopic thermodynamics
Characterized by H = E + PV Associated with anomalies in physical properties
Transition is Intrinsically non-1st order Readily described by robust macroscopic thermodynamics
Characterized by H = E + PV Associated with anomalies in physical properties
Truly exciting both in terms of High pressure physics and chemistry
Understanding Earth’s mantle
But - some re-appraisals are needed
Truly exciting both in terms of High pressure physics and chemistry
Understanding Earth’s mantle
But - some re-appraisals are needed
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
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are needed to see this picture.
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dP
dT=
ΔV
ΔS
Clapyron Slope
€
dP
dT=
ΔV
ΔS
Clapyron Slope
Low-spin iron is an “additional chemical component in the mantle”
Low-spin iron is an “additional chemical component in the mantle”
Fine PrintFine Print Focus on (Mg,Fe)O -
similar behavior for Perovsikte? LS iron has smaller “ionic radius”
D-orbitals directed where oxygen is not Iron sites are non-interacting
Properties in proportion to iron concentration Little difference in EOS of HS and LS iron
“Softening” expected in transition region Increment of pressure causes “normal” strain plus additional strain with HS to LS transition
If spin flip is “fast” compared to acoustic frequency, velocities can decrease
Focus on (Mg,Fe)O - similar behavior for Perovsikte?
LS iron has smaller “ionic radius” D-orbitals directed where oxygen is not
Iron sites are non-interacting Properties in proportion to iron concentration Little difference in EOS of HS and LS iron
“Softening” expected in transition region Increment of pressure causes “normal” strain plus additional strain with HS to LS transition
If spin flip is “fast” compared to acoustic frequency, velocities can decrease
Macroscopic ThermodynamicsMacroscopic Thermodynamics
Gibbs energy: G(P,T,n,x) n is low spin occupation (0 to 1) x is fraction of sites occupied by Fe (0 to 1)
G = Glattice + Gvibration + Gmagnetic + G mixing
Minimize G with respect to n
Gibbs energy: G(P,T,n,x) n is low spin occupation (0 to 1) x is fraction of sites occupied by Fe (0 to 1)
G = Glattice + Gvibration + Gmagnetic + G mixing
Minimize G with respect to n
€
n =1
1+ m(2S +1)eΔH
kTx
€
n =1
1+ m(2S +1)eΔH
kTx
• m = degeneracy (3)• S = Spin state (2)
• H = E + PV
Tsuchiya et al 2006
also: Slichter and Drickamer 1972, Gütlich et al 1979
Theory vs Experiment?Theory vs Experiment?
New Experimental DataNew Experimental Data
Impulsive Stimulated Light Scattering
Impulsive Stimulated Light Scattering
1064 nm
1064 nm
PROBESIGNAL
(Mg,Fe)O 5.6% Fe(100) surface
(Mg,Fe)O 5.6% Fe(100) surface
RubyRuby
Argon
50 microns
Rhenium Gasket
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are needed to see this picture.
Extension to High Temperature?
Extension to High Temperature?
Intrinsic Spin Transition Total
Predicted Seismic Structure
SUMMARYSUMMARY Large anomalies in Vp and Vs for HSLS transition
Macroscopic thermodynamic description works Tested vs pressure and composition High temperature test is needed
Mantle velocity anomalies may be suppressed - dV/dTHSLS > 0 Explanation for lack of mid-mantle tomographic structure?
Perovskite is presumed to have analogous behavior
Large anomalies in Vp and Vs for HSLS transition
Macroscopic thermodynamic description works Tested vs pressure and composition High temperature test is needed
Mantle velocity anomalies may be suppressed - dV/dTHSLS > 0 Explanation for lack of mid-mantle tomographic structure?
Perovskite is presumed to have analogous behavior