Chemical and Physical Properties and Thermal State of the Core - Physics and Chemistry of the Deep Earth - page 243

and reducing conditions provided the refractory
nature of the Earth's core, and under these con-
ditions, Si is a favorable candidate for the light
element of the core. Reaction of metallic iron
and mantle silicates, and dissolution of Si and/or
O in molten iron have been proposed by some
authors (e.g., Rubie et al ., 2004; Takafuji et al .,
2005; Sakai et al ., 2006; Kawazoe & Ohtani, 2006;
Corgne et al ., 2008). On the other hand, the core
formation at lower temperatures favors entry of
volatile light elements, such as S, C, and H, as
candidates for the Earth's core. Thus, studies on
identification of the light elements of the core
could provide very important constraints for for-
mation conditions and processes occurred during
formation of the Earth and planets. Here the re-
cent advances in studies of the Earth's central
regions are reviewed.

(e.g., Murakami et al ., 2004; Oganov & Ono,
2004). The spin transition in the lower mantle
phases may have potential effects on seismic
wave velocities (Crowhurst et al ., 2008; Anto-
nangeli et al ., 2011) and on Mg-Fe partitioning
between the phases in the lower mantle (e.g.,
Sakai et al ., 2009). The spin transition may
also affect the density of magmas under the
lower mantle conditions and the spin-transition
could affect the partitioning of Mg-Fe between
melt and perovskite (Nomura et al ., 2011). Spin
transition in Fe 2 + in the melt could enhance iron
enrichment of the melt, thus producing a dense
magma containing low-spin iron in the melt, as
discussed by Nomura et al . (2011). This could
also enhance the iron enrichment and formation
of dense melt at the base of the lower mantle
producing the ultralow-velocity zone (ULVZ).
The post-perovskite transition may explain
the seismic velocity anomalies in the D'' layer.
The knowledge of this phase boundary can
constrain the structure at the base of the lower
mantle when combined with seismological ob-
servations. Models of the post-perovskite phase
boundary are shown in Figure 8.1. For example,
a double-crossing across the post-perovskite
phase boundary at the base of the lower mantle
was proposed by Hernlund et al . (2005). If this

8.2 Core-Mantle Boundary

8.2.1 A double crossing of the post-perovskite
phase boundary

Recent advances in high-pressure mineral physics
have revealed several new phase transitions in
the lower mantle, such as the spin (e.g., Badro
et al ., 2004) and post-perovskite transitions

Fig. 8.1 The post-perovskite
phase boundary and the
geotherm at the base of the lower
mantle. The cartoon shows a
schematic picture of a slab and
the stable regions of perovskite
(Pv) and post-perovskite (PPv) at
the base of the lower mantle.
A possible double crossing of the
post-perovskite phase boundary;
modified from Hernlund et al .
(2005). A-B, the post-perovskite
phase boundary with double
crossing. Recent phase
boundaries by Tsuchiya et al .
(2004), Mao et al . (2004), and
Shieh et al . (2006) do not show
double crossing. Pv, perovskite;
PPv, post-perovskite. Reproduced
with permission of Nature.

60

Cold slab

Geotherm

A

Pv

Mao et al .
(2004)

80

PPv

Shieh et al . (2006)

100

A

B

120

D''

Outer core

Tsuchiya et al .
(2004)

Modified from Hernlund et al .
(2005)

CMB

B

140

1000 2000 3000 4000

Temperature, GPa