Geoscience Reference
In-Depth Information
Figure 7.11.
Heat flow
versus crustal age for the
continents. The heights of
the boxes indicate the
standard deviation about
the mean heat flow, and
the widths indicate the
age ranges. (After Sclater
et al
.(1980).)
120
100
80
60
40
20
0
0 1000 2000 3000 4000
Age (Ma)
Figure 7.12.
Measured
heat flow
Q
0
plotted
against internal heat
generation
A
0
for (a) the
eastern-U.S.A. heat-flow
province. The straight line
Q
0
=
Q
r
+
DA
0
that can be
fitted to these
measurements has
Q
r
= 33x10
−3
Wm
−2
(b)
(a)
120
120
EW
CA
100
100
BR
C
EUS
80
80
I
60
60
S
SN
and
Y
D
= 7.5 km. (After Roy
et al.
(1968).) (b)
Best-fitting straight lines
for other heat-flow
provinces: CA, central
Australia; B, Baltic shield;
BR, Basin and Range; C,
Atlantic Canada; EW,
England and Wales; EUS,
eastern USA; I, India; S,
Superior Province; SN,
Sierra Nevada; and Y,
Yilgarn block, Australia.
(After Jessop (1990).)
B
40
40
20
20
0
0
0
2
4
6
8
0
2
4
6
8
W m
--3
)
W m
--3
)
A (
µ
A (
µ
0
0
the examples of Sections 7.3 and 7.8. The particularly scattered heat-flow values
measured at ages less than about 800 Ma are evidence of strong influence of
these transient processes and are therefore very difficult to interpret in terms of
the deeper thermal structure of the continents.
In some specific areas known as heat-flow provinces, there is a linear relation-
ship between surface heat flow and surface radioactive heat generation (Fig. 7.12).
Using this relationship, one can make an approximate estimate of the contribution
of the heat-generating elements in the continental crust to the surface heat flow.
In these heat-flow provinces, some of which are listed in Table 7.6, the surface
heat flow
Q
0
can be expressed in terms of the measured surface radioactive heat
generation
A
0
as
Q
0
=
Q
r
+
A
0
D
(7.75)
where
Q
r
and
D
are constants for each heat-flow province.
