Geoscience Reference
In-Depth Information
Table
8.8
Table 8.10
Densities and elastic-wave veloc-
ities of upper-mantle rocks
Density
and
shear
velocity
of
mantle rocks
Rock
V
p
V
s
V
p
/
V
s
ρ
Garnet Iherzolite
3.53
8.29
4.83
1.72
3.47
8.19
4.72
1.74
3.46
8.34
4.81
1.73
3.31
8.30
4.87
1.70
Dunite
3.26
8.00
4.54
1.76
3.31
8.38
4.84
1.73
Bronzitite
3.29
7.89
4.59
1.72
3.29
7.83
4.66
1.68
Eclogite
3.46
8.61
4.77
1.81
3.61
8.43
4.69
1.80
3.60
8.42
4.86
1.73
3.55
8.22
4.75
1.73
3.52
8.29
4.49
1.85
3.47
8.22
4.63
1.78
Jadeite
3.20
8.28
4.82
1.72
Clark (1966), Babuska (1972), Manghnani
and Ramananotoandro (1974), Jordan (1979).
Table 8.9
Densities and elastic-wave veloci-
ties in upper-mantle minerals
given density, eclogites tend to have lower shear
velocities than peridotite assemblages.
The 'standard model' for the oceanic litho-
sphere assumes 24 km of depleted peridotite --
complementary to and forming contemporane-
ously with the basaltic crust -- between the crust
and the presumed fertile peridotite upper man-
tle. There is no direct evidence for this hypo-
thetical model. It is a remnant of the pyrolite
model. The lower oceanic lithosphere may be
much more basaltic or eclogitic than in this sim-
ple model, and it might not have formed con-
temporaneously. Buoyant, refractory and olivine-
rich lithologies may have accumulated in the
shallow mantle for billions of years (Gyr). Basalts
can pond beneath plates that are under lateral
compression.
V
p
V
s
ρ
(g/cm
3
)
Mineral
(km/s)
V
p
/
V
s
Olivine
Fo
3.214
8.57
5.02
1.71
Fo
93
3.311
8.42
4.89
1.72
Fa
4.393
6.64
3.49
1.90
Pyroxene
En
3.21
8.08
4.87
1.66
En
80
3.354
7.80
4.73
1.65
Fs
3.99
6.90
3.72
1.85
Di
3.29
7.84
4.51
1.74
Jd
3.32
8.76
5.03
1.74
Garnet
Py
3.559
8.96
5.05
1.77
A1
4.32
8.42
4.68
1.80
Gr
3.595
9.31
5.43
1.71
Kn
3.85
8.50
4.79
1.77
An
3.836
8.51
4.85
1.75
The perisphere
Uv
3.85
8.60
4.89
1.76
Sumino and Anderson (1984).
The cratonic lithosphere is chemically buoyant
relative to the underlying mantle, a result of melt
depletion. The shallow mantle elsewhere may
