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measured perovskite sample
in-situ
in a DAC
under thermodynamic stability field of perovskite
sample or not. The possible reason why their un-
certainty of
G
0
is larger than that in Murakami
et al
. (2007) by one order of magnitude could be
due to stress condition of the measured perovskite
with/without laser annealing in a DAC.
There are no available high-pressure shear wave
velocity experimental data on (Mg, Fe)SiO
3
per-
ovskite, and the possible effect of iron spin transi-
tion in pv (Badro
et al
., 2004) has yet to be revealed
experimentally. Given that the iron content in pv
may be only
G' = 2.0
G' = 1.8
7.8
G' = 1.56
7.6
G' = 1.4
7.4
7.2
7.0
6.8
6.6
MgSiO
3
perovkskite
6.4
0
20
40
60
80
100
120
6mol%(Murakami
et al
., 2005),
much lower than in coexisting fp in the lower
mantle, its influence on the elasticity is expected
to be very limited. Recent computational study
demonstrates that the change in the spin state
of Fe
2
+
and Fe
3
+
has little effect on the elastic
properties of pv (Stackhouse
et al
., 2007).
∼
Pressure (GPa)
Fig. 6.5
Shear wave velocity profile of MgSiO
3
perovskite as a function of pressure at 300 K (black
circles) from Murakami
et al
. (2007a). Third-order
finite strain fit are shown by black line. White circle
and diamond indicate previous experimental results at
ambient conditions (Sinogeikin
et al
., 2004;
Yeganeh-Haeri, 1994). Dashed lines show the shear
wave velocity profiles extrapolated using previously
reported values of
G
0
of 2.0 (Li & Zhang, 2005) and 1.8
(Sinelnikov
et al
., 1998) by ultrasonic interferometry,
and 1.4 for comparison. Upward and downward
triangles indicate the recent theoretical calculations by
first principles at 0 K (Tsuchiya
et al
., 2004) and 298 K
(Oganov
et al
., 2001).
6.3.2 MgSiO
3
post-perovskite
The Earth's core-mantle boundary (CMB)
between crystalline silicate rock and molten iron
alloy is believed to be the interface with the
largest contrast in various physical properties
(e.g., density, elastic moduli, electrical conduc-
tivity) within the Earth's interior, and different
materials (molten iron) and silicates may interact
at or near this boundary (Davis & Gurnis, 1986;
Young & Lay, 1987; Knittle & Jeanloz, 1991; Lay
et al
., 1998). The D
layer, just above the CMB,
has therefore attracted a great deal of interest
in seismology and mineral physics because this
layer may play a key role in the dynamics and
thermal evolution of the Earth's mantle. Here,
I briefly outline the seismic signature observed
at the base of the mantle and its interpretations
based on recent high-pressure elasticity data.
Advances in seismology have provided some
unusual and puzzling seismic characteristics of
the D
region incluidng a discontinuity in seis-
mic wave velocities (Lay & Helmberger, 1983),
anomalous shear wave anisotropy (Mitchell &
Helmberger, 1973), large lateral velocity varia-
tions (Garnero
et al
., 1993) and the ultralow
velocity zones (Garnero
et al
., 1998). The D
(Tsuchiya
et al
., 2004) and ambient temperatures
(298 K) (Oganov
et al
., 2001).
Jackson
et al
. (2005) have conducted high-
pressure Brillouin measurements on aluminous
MgSiO
3
perovskite with 5 wt% Al
2
O
3
to 45 GPa
using the polycrystalline starting perovskite sam-
ples pre-synthesized by the multi-anvil large vol-
ume press, yielding the
G
0
=
0.2. Although
the experimental error of
G
0
in Jackson
et al
.
(2005) is relatively high, the results by Murakami
et al
. (2007) on the pure MgSiO
3
perovskite are
in agreement with that by Jackson
et al
. (2005)
within the experimental uncertainties, indicat-
ing the shear velocity of perovskite is relatively
insensitive to Al content. Distinct differences
of the Brillouin scattering measurement proce-
dure between Murakami
et al
. (2007) and Jack-
son
et al
. (2005) is whether they synthesized he
1
.
7
±