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COMPRES 2006 Snowbird, UtahDavid Walker, Lamont-Doherty Earth Observatory, Columbia U.
Why ever would the Earth’s core leak?
Why ever would the Earth’s core leak?
With Simon Clark, Martin Kunz, Mike Walter and a With Simon Clark, Martin Kunz, Mike Walter and a COMPRES-supported cast of thousandsCOMPRES-supported cast of thousands
With Simon Clark, Martin Kunz, Mike Walter and a With Simon Clark, Martin Kunz, Mike Walter and a COMPRES-supported cast of thousandsCOMPRES-supported cast of thousands
(NSF CSEDI+2 progress report)
Chondritic Evolution
Evolution of OC
187Os/
188 Os
0.100 0.120 0.140
0.119820
0.119830
0.119840
0.119850
0.119860
0.119870
Mix
ing
186
Os
/188
Os
Mauna Loa Loihi Koolau Mauna Kea Kilauea Hualalai Kohala Siberia Gorgona
solidsolidmantlemantle
InnerInnercorecore
LiquidLiquid metal metalouter coreouter core
Core-Core-flavoredflavoredplumeplume
atmosphereatmosphere
A.Brandon, R.J.Walker et al. (2003)
Some plume basalts show correlated Os anomalies.
OsPtPt
DescendingDescendingslabslab
Sr, O, Nd recycling signal
187Re-driven187Re-driven19
01
90 P
t-dr
iven
Pt-
driv
en1
90
19
0 Pt-
driv
enP
t-dr
iven
Maybe Re?
Manghnani and Yagi
Is the core really leaking?Is the core really leaking?
Yes, perhaps: Os isotopesHawaiian plume Fe/Mn & Ni
Perhaps not: radiogenic Sr/Os correlation
What could drive it?What could drive it?What could drive it?What could drive it?
FeO solution reaction
-10
-8
-6
-4
-2
0
2
4
6
8
10
0 100 200 300 400
P kilobars
DV
cc/
mo
leDAClimit
O2 fromDaresbury
O’Neill et al.Rubie et al.Multi-anvil
DVsolution = LiquidVFeO – CrystalVFeO
What determines oxygen solubility(P)?
Solubility Solubility extremely extremely
limitedlimited
Solubility Solubility extremely extremely
limitedlimited
Manghnani and Yagi
Thermal exsolution of a floating ‘slag’(We know the Earth is cooling)
(A year in the lab can save you an hour in the library!)(A year in the lab can save you an hour in the library!)
But we still need to measureOxygen solubility in Fe liquid at high P,T
But we still need to measureOxygen solubility in Fe liquid at high P,T
Does it reach 2% or 20%?
Fe FeO
100 microns
X-ray absorptiontransmission
imaging in situ
X-ray beamX-ray beam
How to measure Oxygen solubility in molten Fe
at a megabar?
[Underway withCOMPRES support
for the ALS 12.2.2 team]
Lasermelting
http://xraysweb.lbl.gov/bl1222/home.htm
Experiments at ALS/LBL With Mike Walter*, Simon
Clark, Martin Kunz, and many others
*
X-rays in
LBL ALS Station 12.2.2
Remote and/orautomated pneumatic
P ramping
Remote and/orautomated pneumatic
P ramping
Double-sidedLaser heatingDouble-sidedLaser heating
X-rays in
LBL ALS Station 12.2.2
Double-sided pyrometryDouble-sided pyrometry
High-resolution imaging
Laser
FeO crystals in 100 hole
DAC gasket image
In situ DAC X-Radiographic Imaging (XRI)
Gasket
Fe
FeO
X-ray density for chemical analysis!
Thin CdS phosphor
CCD and optics
FeFeO
Liq
Itrans
Fe
FeO
Liquid %O2
Single in situ property (Itrans)needed to characterize
chemistry along abinary join.
Absorption(ع) &/or emission
Melting shows erosion
50 kilobars
FeS
Fe
What about Fe-FeO?
Fe-FeS after first melting
at ~50 kbar
48000
50000
52000
54000
56000
58000
60000
0 10 20 30 40 50 60
Position (Pixels = ~1.5 microns)
6 K
V X
-ray
co
un
ts
Expected liquidUsselman, 1975
First Liquid
Fe
FeS
Topography convolved with chemistry
-and-resolution limited by
phosphor sharpness and sample preparation
It seems to work!
550 kilobars550 kilobars
FeO
Fe
No erosion on melting!
Consistent with the DAC results of Takafuji et al. (2005) <6%Consistent with the DAC results of Takafuji et al. (2005) <6%
Are there other solutions to the problem?
Oxygen solubility does not appear to be high enough to be interesting.
Lumpy D′′ probably not
exsolved,floating slagon molten Fe of the outer
core
mantlecore
low [Fe]
Toroidal magnetic field in the outer core generates local anodic
and cathodic areas at the CMB ~ 1 V
Could this drive any electrochemicaltransfers across the CMB?
(See Abby Kavner’s forthcoming paper in EPSL)(See Abby Kavner’s forthcoming paper in EPSL)
What does the presence of life do for us?What does the presence of life do for us?
Oxidative corrosion of coremantle
Core signal generated by recycled oxidized crust.Contaminated plume source
D” includesCMB magma
chambers
N2 + O2 Oxidized crust
Iron meets oxygen!
When oxygen does not dissolve in iron.
rustysurface rustysurface Bright inner coreBright inner core
solidsolidmantlemantle
InnerInnercorecore
Liquid metalLiquid metalouter coreouter core
Core-Core-flavoredflavoredplumeplume
N2 + O2
DD" with magmatic" with magmatictitration chamberstitration chambers
Most effective and quick if oxygen solubility low
Revenge of the plants!
OxidizedOxidizedslabslabOs-Sr-Nd-O signal of
recycled crust not ashow stopper. It is the
key to the deliverymechanism for the corrosive reaction.