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10
3040 K
3040 K
3
8
2840 K
6
2
2840 K
2430 K
4
1
2430 K
2
2320 K
2320 K
0
0
2
1
0
2
1
0
Δ
logfO 2 (IW)
Δ
logfO 2 (IW)
(a)
(b)
Reducing
8
10
27 GPa, 2600 K
27 GPa, 3000 K
8
6
6
93 Gpa, 3000 K
139 GPa, 3000 K
O
4
4
Si
2
2
0
0
20
60
100
140
0
4 8 12
O in liquid iron (wt %)
Pressure (GPa)
(c)
(d)
Fig. 8.2 (a) and (b) The effect of fO 2 and temperature on the solubility of Si and O in molten iron coexisting with
MgSiO 3 perovskite, respectively at 27 GPa (Kawazoe & Ohtani, 2005). Reproduced with permission of Springer.
(c) The pressure effect at 3000 K on the solubility of O and Si in molten iron (Sakai et al ., 2006), Reproduced with
permission of the American Geophysical Union and (d) The solubility of Si and O in molten iron at high pressure
and temperature. The solubility of both elements increases with increasing pressure and temperature. The outer
core density deficit (cdd in %) is given in (d).
of these elements in the outer core. During the
secular cooling of the outer core, exsolution of
these elements from molten iron and crystalliza-
tion, flotation, and accumulation of FeO could
have occurred at least locally at the outermost
layer of the outer core (Buffet et al ., 2000; Helf-
frich & Kaneshima, 2010), and high O fugacity
conditions could have been achieved at the CMB.
Therefore, the existence of ferric/ferrous-enriched
perovskite at the mantle side of the CMB proposed
by Mao et al . (2006) could develop when there was
a stratification with local FeO enrichment at the
outermost region of the outer core during cooling
of the core (Helffrich & Kaneshima, 2010).
8.3
Outer Core: Melting and Melt Properties of
the Core Materials
8.3.1 Light elements in the outer core and core
formation process
Recent analyses of the equation of state and the
sound velocity of the solid and liquid iron and
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