Geoscience Reference
In-Depth Information
Figure 3.17.
Synthetic magnetic-anomaly profiles generated
by a ridge at 40
◦
S, spreading east-west with a half-rate of
3cmyr
−1
. The magnetized crust subsequently moved
northwards to the latitudes shown, leaving the blocks
striking north-south. Note that the shapes of the anomalies
depend upon the present latitude and that, if the magnetized
crust moves across the equator, positively magnetized blocks
give rise to negative anomalies. Black denotes periods of
normal magnetic field; white denotes periods of reversed
field. Numbers are anomaly numbers (see Fig. 3.14). (From
McKenzie and Sclater (1971).)
Observed at 40
°
N
Observed at 20
°
N
Observed at 20
°
N, magnetic equator
Observed at equator
Observed at 20
°
S
1000
nT
Observed at 40
°
S
27
28 29
30 31
32
33
100 km
Figure 3.18.
Synthetic magnetic-anomaly profiles
produced by the magnetized blocks now striking
east-west at 15
◦
N. The magnetized oceanic crust was
formed at 40
◦
Sbymid-ocean ridges spreading at
3cmyr
−1
half-rate and striking due north, N45
◦
E and
N45
◦
W. Note that the anomalies for the N45
◦
E ridge
and the N45
◦
W ridge are exactly the same. Numbers
are anomaly numbers (see Fig. 3.14). (From McKenzie
and Sclater (1971).)
Ridge striking due north
Ridge striking N45
E
°
1000
nT
Ridge striking N45
°
E/
27 28
29
30
31
32
33
100 km
