Geoscience Reference
In-Depth Information
Table 4.13
Nd isotopic data of the basaltic and granitic
end-members
147
Sm/
144
Nd
143
Nd/
144
Nd
[Nd] (ppm)
Rhyolite
40
0.11
0.5115
Basalt
15
0.17
0.5128
basalt-rhyolite mixtures. Plot the mixing line with its end-members in the isochron
diagram and “age” the samples by 1 Gy and 2 Gy. Calculate the apparent ages of the
alignment for 0, 2, and 3 Gy into the future. Devise a strategy to decide whether an
alignment in the isochron diagram is a mixing line or a true isochron.
16. Sketch out the evolution of the Bulk Silicate Earth (
147
Sm/
144
Nd
=
0.1967 and
143
Nd/
144
Nd
0.512638 today) in a
143
Nd/
144
Nd vs.
t
evolution diagram between
2 Ga and the present and the evolution of a crustal rock formed at 2 Ga from the
primitive mantle with a
147
Sm/
144
Nd ratio of 0.11. What is the modern
=
ε
Nd
of this
rock?
17. Compare the evolution diagram
143
Nd/
144
Nd vs.
t
and the isochron diagram
143
Nd/
144
Nd vs.
147
Sm/
144
Nd. Plot the points representing the modern depleted man-
tle (
147
Sm/
144
Nd
0.222 and
143
Nd/
144
Nd
=
=
0.51312) and a crustal sample with
147
Sm/
144
Nd
0.12 and
143
Nd/
144
Nd
0.5111. First, find graphically in each dia-
gram the model age at which the protolith of this crustal sample was extracted from
the depleted mantle. Second, derive a common expression that will let you calculate
this model age with precision.
=
=
References
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,
95
, 17 605-17 629.
♠
Arnold, J.R. and Libby, W. F. (1949) Age determination by radiocarbon content: Checks
with samples of known ages.
Science
,
110
, 678-680.
♠
Bateman, H. (1910) Solution of a system of differential equations occurring in the theory
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Proc. Cambridge Phil. Soc.
,
15
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238
U-
230
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