Geoscience Reference
In-Depth Information
the bottom 1000 km of the mantle there are
further phase changes in
perovskites
, stishovite
and the
spin-state of FeO
. Below about 700
km the density of silica-rich basalt (NMORB)
exceeds that of pyrolite, if it can get through
the subduction barrier.
The lower mantle may
be enriched in both FeO and SiO
2
com-
pared to pyrolite and the upper man-
tle
. This has been a controversial issue, based
partly
on
fitting
equations
of
state
to
lower
mantle
properties,
ignoring
the
above
issues,
i.e.
assuming
chemical
and
phase
homogene-
ity,
and
assuming
an
adiabatic
temperature
gradient.
