Geology Reference
In-Depth Information
N
20 000 nT
12 W
10 000 nT
0
100m
0
8 W
4 W
0
4 E
Conductor outline
Magnetics
8 E
Fig. 7.25
Vertical field ground magnetic
anomaly profiles over a massive sulphide
ore body in Quebec, Canada.The shaded
area represents the location of the ore
body inferred from electromagnetic
measurements. (After White 1966.)
12 E
In academic studies, magnetic surveys can be used in
regional investigations of large-scale crustal features, al-
though the sources of major magnetic anomalies tend to
be restricted to rocks of basic or ultrabasic composition.
Moreover, magnetic surveying is of limited use in the
study of the deeper geology of the continental crust be-
cause the Curie isotherm for common ferrimagnetic
minerals lies at a depth of about 20 km and the sources of
major anomalies are consequently restricted to the upper
part of the continental crust.
Although the contribution of magnetic surveying to
knowledge of continental geology has been modest,
magnetic surveying in oceanic areas has had a profound
influence on the development of plate tectonic theory
