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Mineralogical Model of the Lower Mantle: Constraints from Elasticity
Motohiko MurakamiTohoku University
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Acknowledgements
Jay D. Bass (University of Illinois) Stanislav V. Sinogeikin (University of Illinois)Holger Hellwig (University of Illinois)Jie Li (University of Illinois)Zhang Jing (University of Illinois)Nagayoshi Sata (JAMSTEC)Yuki Asahara (SPring-8)Yasuo Ohishi (SPring-8)Naohisa Hirao (SPring-8)Kei Hirose (Tokyo Tech)
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http://www.lpl.arizona.edu/grad/fieldtrips/2007f-southernnewmexico/
SiO246%
MgO39%
FeO8%
Al2O33%
CaO3%
wt%
Mineralogical model of upper mantle“Peridotitic” upper mantle
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Is Earth’s mantle chemically homogeneous?
lower mantle
upper mantle
core
lower mantle
upper mantle
core
Homogeneous mantle(Peridotitic)
Heterogeneous mantle(Si-rich lower mantle?)
? ?
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Recent seismological views in Earth’s deep interior
(Garnero & McNamara, 2008)
Large Low-Shear-Velocity Provinces (LLSVPs)Ultra Low Velocity Zones (ULVZs)
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1D seismological model in Earth’s interior
Mineralogical modeling of deep mantle
PREM
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Challenges for sound velocity measurements
Lower mantle
mineralogy
Pressure135 GPa
Temperature
>2500 KComposition
Fe, Al..
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Previous work on MgSiO3 pv
(Li & Zhang, 2005)
up to ~9 GPa by ultrasonic measurement
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Diamond Anvil Cell (DAC) apparatusProbe laser (514.5 nm, 532 nm)6-pass tandem Fabry-Perot interferometer
High-pressure Brillouin scattering system
Pressure High-Pressure sound velocity
Prof. Bass(UIUC)
Diamond anvil cell
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(Murakami et al., 2007)
Shear velocity of MgSiO3 pvdG/dP (G’0) =
1.56
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MgSiO3 perovskite to 100 GPa
(Murakami et al., EPSL, 2007)
MgO to 130 GPa
(Murakami et al., EPSL, 2009)
MgSiO3 ppv to 172 GPa
(Murakami et al., EPSL, 2007b)
Pressure High-Pressure sound velocity
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Challenges for sound velocity measurements
Lower mantle
mineralogy
Pressure135 GPa
Temperature
>2500 KComposition
Fe, Al..
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Composition
Effect of chemistry
High-pressure data are still limited
Fe, Al…
(Mg,Fe)O fp Al-MgSiO3 pvCrowhurst et al. 2008Marquardt et al., 2009
Jackson et al. 2005
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(Mg0.92Fe0.08)O: 120 GPa, 300 KAl-MgSiO3 pv: 124 GPa, 300 K
(4 wt% Al2O3)
Shear wave velocity measurementsfor fp and Al-pv
Brillouin System at SPring-8
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Brillouin data (Mg0.94Fe0.08)O86 GPa
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Shear velocity of (Mg,Fe)O
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Effect of spin transition on the elasticity
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Brillouin data of aluminous MgSiO3 pv95 GPa
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Shear velocity of Al-MgSiO3 pv
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composition G0 (GPa)
G’0 pressure reference
Al-MgSiO3 (4 wt%)
166(1) 1.57(5) 124 GPa This study
Al-MgSiO3 (5 wt %)
165(2) 1.7(2) 45 GPa Jackson et al. 2005
MgSiO3 173(1) 1.56(4) 96 GPa Murakami et al. 2007
Effect of Al on the elasticity of pv
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MgSiO3 pv, 96 GPaMgO, 130 GPa
Al-MgSiO3 pv, 124 GPa(Mg,Fe)O, 120 GPa
MgO-SiO2-FeOCompositi
on
(Murakami et al. 2007)
(Murakami et al. 2009)
-Al2O3
(Murakami et al. 2012)
(Murakami et al. 2012)
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Modeling of lower mantle mineralogy
Al-MgSiO3 pv, 124 GPa(Mg,Fe)O, 120 GPa(Murakami et al. 2012)
(Murakami et al. 2012)
System MgO-SiO2-FeO-Al2O3
FormalismStixrude & Lithgow-Bertelloni, 2005
Geotherm
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Lower mantle geothermsTwo extreme models
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Modeling of lower mantle mineralogyWhole mantle convection geothermal model
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Modeling of lower mantle mineralogyLayered mantle convection geothermal model
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Pv95%
Fp5%
Mineral proportion (vol%)
Mineralogical Model of Lower Mantle
Pv80%
Fp20%
Mineral proportion (vol%)
Peridotitic lower mantle Perovskititic lower mantle
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lower mantle
upper mantle
core
PerovskititePv
95%
Fp5%
Mineral proportion (vol%)
Perovskitic lower mantle
SiO2-enriched lower mantle
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lower mantleupper mantle
core
Early Earth Current Earth
Layered mantle convectionChemically stratified mantleFractional crystallization
Evolution history of the mantle
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How to maintain such chemical stratification?
Big question/problem
(Brandenburg et al., 2008)
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Challenges for sound velocity measurements
Lower mantle
mineralogy
Pressure135 GPa
Temperature
>2500 KComposition
Fe, Al..
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Technical development for sound velocity measurements under H-TTemperatu
re
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Brillouin scattering + XRD + Laser heatingSimultaneous measurement system for Vs,p, V and T
(Murakami et al. 2009)
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XRDLaser heatingBrillouin spectrum
TemperatureMgO at 50 GPa, 2500 K
Sound velocity under high P-T
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(Chantel et al. 2012)
High-T data on (Mg,Fe)SiO3 pv
High-T elasticity data support our conclusion
Ultrasonic method with large volume pressup to 25 GPa and 1200 K
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Toward better understanding..
*Combined effect of Fe & Al on the elasticity of Pv
*Data quality improvement of the high-T data
*Effect of spin-transition of iron in Pv on the elasticity
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We have determined the sound velocities of MgSiO3 perovskite,MgO, (Mg,Fe)O and Al-MgSiO3 perovsktie under lower mantle pressure conditions
Mineralogical modeling using obtained results strongly indicatesthe perovskitic lower mantle.
Development of new Brillouin spectroscopy at high PT enables usto explore the sound velocities under lower mantle condition.
Summary