CIDER experience

• Attended 2004 lecture and tutorial session• Very useful for my education• Post-perovskite (ppv) fever• Changed thesis to “Geophysics and Geochemistry

of Iron in the Core-Mantle Boundary and Core”• More recently have been using on-line lectures as

a resource for class I co-taught this winter on Earth Structure

• Still working on ppv…

Implications of the Fe-rich ppv at CMB

• Possible explanation for ULVZ

• Multiple ppv structures due to compositional differences, analogous to multiple pyroxene structures in the crust

• Different Fe/Mg partitioning from Fe-poor ppv

Implications of the Fe-rich ppv at CMB

• Possible explanation for ULVZ

• Multiple ppv structures due to compositional differences, analogous to multiple pyroxene structures in the crust

• Different Fe/Mg partitioning from Fe-poor ppv

Fe in ULVZ

• Fe-rich ppv has low enough Vs to explain the depression

of velocity in ULVZ

VP, km/sec VS, km/sec PREM, mantle side of CMB 13.72 7.26 0.30 ULVZ (Thorne, JGR 2004) 12.35 5.08 0.40 Fs40 ppv at 130 GPa-300 K 12.72 4.86 0.41 Fs40 ppv at 130 GPa-3000 K 11.91 4.05 0.43

• Possible explanation for ULVZ

• Multiple ppv structures due to compositional differences, analogous to multiple pyroxene structures in the crust

• Different Fe/Mg partitioning from Fe-poor ppv

Implications of the Fe-rich ppv at CMB

PmmaCmcm

Structure of Fe-rich ppv differs from Fe-poor ppv

Cmcm fits the data but not as well as Pmma

Fe0.4Mg0.6SiO3

x

zy .

Two different Fe sites in Fe-rich ppv

• Pmma– M1 = Fe0.25 Mg0.75, (30% of Fe)

– M2 = Fe0.55 Mg0.45, (70% of Fe)

Lin et al, Nature Geoscience 2008

• SMS shows two predominant sites, consistent with the XRD results?

Intermediate spin?

Implications of the Fe-rich ppv at CMB

• Possible explanation for ULVZ

• Multiple ppv structures due to compositional differences, analogous to multiple pyroxene structures in the crust

• Different Fe/Mg partitioning from Fe-poor ppv

Fe-Mg partitioning

Murakami et al, GRL 2005

Kobayashi et al, GRL 2005

mw

silicate

MgFe

MgFeK

)/(

)/(

Auzende et al, EPSL 2008

Reaction between ppv, mw, and Fe. Core undersaturated in Si and O? Iron-depletion at base of mantle? Knittle and Jeanloz, Science 1991, Takafuji et al, GRL 2005, Sakai et al, GRL 2006, Asahara et al, EPSL 2007, Ozawa et al, GRL 2008

Does partitioning depend on Fe content?

From Auzende et al, EPSL 2008