Geoscience Reference
In-Depth Information
Figure 8.11.
(a) The
S-wave velocity profile of
the upper mantle
compared with the phases
and transition zones for
olivine in the upper
mantle. (After McKenzie
(1983). Copyright (
C
(a)
) 1983
by Scientific American
Inc. All rights reserved.)
(b) Phase transformations
(shaded) for olivine in the
mantle: olivine (
)
through wadsleyite (
)
and ringwoodite (
)to
perovskite (pv) and
magnesiow ustite (mw).
The major seismic
discontinuities at 410 and
670 km as well as the
discontinuity at 520 km
correspond to these
phase transformations.
Dark grey band, upper
mantle adiabat with a
potential temperature
of ∼1500-1600 K.
(b)
changes take place coincide with those at which the seismic velocity increases
more rapidly. The two main phases in the lower mantle, magnesiowustite and
Mg-perovskite, have been shown experimentally to have melting temperatures of
over 5000 and 7000 K, respectively. This means that the lower mantle has always
been solid (Section 7.7).
