Greinar (Vísindafélag Íslendinga) - 01.01.1977, Side 81

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strain. The result is at any rate that, in a 10 km thick layer,
the velocity was raised from that of “seismic” sial to that of
the lower continental crust (“intermediate layer”). This sug-
gests that Conrad marks a deeper layer in which certain physi-
cal changes have taken place. For brevity we might provisori-
ly call these changes “flowage”. The fact that Conrad is clear
in Europe, while difficult to detect in North America, is then
by reference to the Jutland case, not quite unexpected on the
background of the quite different strain- or tectonic histories
of the two continents, at least since Cambrian time: The Con-
rad is clear where strain and “flowage” has moved it up to
a new relative equilibrium in a not too remote past.
Magnetization in seismic layers. In Chapter 4, we concluded
that “flowage” through geologic time intervals may systemat-
ically increase magnetization by alignment of domains, and
that at least parts of Layer 3 in Iceland may in that way have
acquired strong magnetization — one or two orders of magni-
tude above the normal for basalts.
It is now natural to face something similar for such seismic
layers which are due to “flowage”. This would apply especially
to deeper layers in which the temperature, however, is below
the Curie point of the dominant magnetic mineral. For magne-
tite, temperatures of even 400—500° C would then come into
consideration. This w'ould mean maximum depths of 12—15
km for continental areas and 8—10 km for the oceanic ones.
With this in mind, we have at least in the Oceanic Layer a
very extensive one, covering 60—70% of the earth’s surface, in
which strong magnetization might possibly be found. As this
layer is capable of flowage, such stress fields as we studied in
Chapter 3, might give a systematic temporary alignment of
domains. The magnetic field, so formed, could hardly con-
tribute much to the geomagnetic field. Nor do we suggest that
the west drift of the geomagnetic anomalies is of this origin.
But we mention this possible layer of strong magnetization,
if in future studies some details of the global stress fields
of Chapter 3, showed a correlation with some magnetic ano-
malies.