Chemical and Physical Properties and Thermal State of the Core - Physics and Chemistry of the Deep Earth - page 251

of light elements needs to be considered. We need
more precise experimental data on the melting
temperature of pure iron and iron-light-element
systems.
Figure 8.10 shows the temperature profile of
the core estimated by Terasaki et al . (2011) based
on the Fe-Si-O system. The upper and lower
bounds of the ICB temperature correspond to
the liquidus and solidus temperatures at ICB
pressure, respectively. The liquidus temperature
of Fe 75 O 5 S 20 at 136 GPa was determined to be
3600

Fe 75 O 5 S 20 alloy

4000

Fe Liq

+

Liquidus
Solidus

Melting of pure Fe

3000 Liq

Fe + FeO + Liq

2000

Fe + FeO + Fe 3 S

200 K, which gives a lower bound of the
temperature at CMB (Figure 8.10). The solidus
and liquidus temperatures at 330 GPa, obtained
using extrapolation by the Simon equation, are
4380

±

1000

0 40 80 120 160

P, GPa

± ±

350 K, respectively, pro-
viding the lower and upper bounds of temperature
at the ICB for this composition. The ICB tem-
perature was estimated previously by using the
melting temperature of pure iron determined by
various procedures, and the present upper bound
of the ICB temperature of 5630

200 and 5630

Fig. 8.9 The phase and melting relations of Fe 75 O 5 S 20
alloy in the Fe-O-S system determined by Terasaki
et al . (2011). The liquidus phase is hcp-Fe, and the
second liqudus phase is FeO. Fe 3 Sisconsumedfirstat
the solidus temperature. The solidus temperature of
this system is very close to the eutectic temperature of
the Fe-Fe 3 S system, indicating that the effect of FeO in
the melting relation of the Fe-O-S system is very
small. Reproduced with permission of Elsevier.

± 350 K is lower

than the previous estimate; i.e. ∼ 170 K lower

than that (T mFe = 5800 K) estimated by the di-

amond anvil cell experiment (Ma et al ., 2004),

2007; Kamada, 2011), and the effect of FeO pres-
ence on the solidus temperature seems to be
negligible under megabar conditions.

6000

hcp-Fe (Ma et al ., 2004)

T L ad

(c) Constraints on temperature of the core based
on melting experiments The melting relations
can be used to estimate the thermal state of
the core. The temperatures at ICB and CMB
can be estimated by using the melting relations
of the iron-light-element systems. The melting
temperature of iron has been calculated to be
6700

5000

Liquidus

4000

T s ad

3000

Solidus

600 K at the ICB (e.g., Alfe et al ., 1999),
which is close to the melting temperature de-
termined by the shock experiments (Brown &
McQueen, 1980, 1986; Yoo et al ., 1993; Nguyen
& Holmes, 2004). The ICB has been assumed to be
the solid-liquid phase boundary and the melting
temperature of pure iron has been used to con-
strain the ICB temperature. However, the temper-
ature at the ICB, as estimated from the melting
temperature of pure iron, remains uncertain and
varies from 4000 to 7000K. In addition, the effect

±

CMB ICB

350 100 150 200 250 300

Pressure, GPa

Fig. 8.10 The temperatures at the ICB and CMB
estimated based on the liquidus and solidus
temperatures of the Fe-Si-O system by Terasaki et al .
(2011). See the text in detail. T L ad and T S ad are the
adiabatic temperature profiles decompressed from the
liquidus and solidus temperatures at ICB, respectively.
Reproduced with permission of Elsevier.