24 Origin and Morphology of Ocean Basins
26 million years (Fig. 1.9). It can be argued from physical principles that the depth of
the sea floor on the spreading flanks of the Ridge should be a simple function of age:
depth below crest = k . -V age.
(1.1)
From the relationship given above, we can evaluate k as follows:
k = 1000 and k = 2000
-{fO
-V 10+26 '
which comes out as k '" 320, when depth is in meters and age in million years. If this
is correct, we can calculate the average age of the deep-sea floor from its average
depth (after correcting for sediment cover). For an average (corrected) basement
depth of 5000 m (= 2400 m below Ridge crest), we obtain an age of 60 million years,
which is indeed close to the average age of the sea floor.
2
E
oX
4
6
0
8
'"
.to
c~
=>0;~~
.2E4
LLg
(U~
Q)::1.
:I:~
00
4.0
a
0 0
a
a a
0
o ¢ 0
50
~
b
-
....
•
50
C GROUP VELOCITY
OF RALEIGH WAVES
Sea Floor Age (million years)
WATERDEPTH
o
100
1S0
HEAT FLOW
•
.-_--.....
100
150
Fig. 1.9. a- c. Observations illustrating the cooling of the lithosphere at mid-oceanic ridges. a After
J. G. Sclater et a!. , 1971. "reliable mean values" b After Sclater et a!., 1976 (hars); and Sclater and
Francheteau 197 1 (dots) . c Seismic waves ve locities increase with cooling, after Yoshii (1975) and
Forsyth (1977) cire/cs and dots. [E. Seibold et a!., 1986, The sea floor. Japanese edition ]