By studying sediments of various ages, we should be able to draw some inferences about the
rates of continental growth.
Goldstein and O'Nions (1984) found that the mean crustal
residence time (
τ
DM
, calculated from
147
Sm/
144
Nd and
143
Nd/
144
Nd) of the river particulates they
studied was 1.7 Ga, which they interpreted as the mean age of the crust being eroded.
However, they estimated the mean crustal residence time of the entire sedimentary mass to
be about 1.9 Ga.
Figure 16.13 compares the stratigraphic age
*
of sediments with their crustal
residence ages.
Note that in general we expect the crustal residence age will be somewhat
older than the stratigraphic age.
Only when a rock is eroded into the sedimentary mass
immediately after its derivation from the mantle will its stratigraphic (