Rit (Vísindafélag Íslendinga) - 01.06.1967, Blaðsíða 102

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versed polarization. The width of these blocks would depend
on the length of any particular geomagnetic epoch.
The reversals during the last 3—4 million years have now
been determined with some accuracy (Cox, Doell and Dal-
rymple 1964, Doell and Dalrymple 1966) wherehy theore-
tical magnetic profiles can be calculated according to the Vine-
Matthews hypothesis. The agreement between these and ob-
served profiles from various parts of the earth is remarkahle
and leaves no doubt that magnetic anomalies correspond to
the epochs of the earth’s magnetic field. (Vine 1966, Pitman
and Heirtzler 1966). In the following I will assume that the
Vine-Matthews hypothesis is the correct explanation of most
magnetic anomalies in the axial zones of the ridges, includ-
ing the surveyed area on the Reykjanes-Ridge.
Recause of Iceland’s geographical position and the linearity
of the eruptions, it is popular among scientists to assume
that with some modifications, the volcanic activity, past and
present, which can so conveniently he studied here, is repre-
sentative for what is going on at the mid-ocean ridges. New
evidence concerning their creation is therefore important to
us. I have tried to use the profiles published by Vine (1966)
to draw some conclusions about the ridges for comparison
with volcanism in Iceland.
In Vine’s model the boundaries between the blocks are ver-
tical and the thickness and the rate of production of the
magnetized layer are constant. The total width of the parts
of the layer, corresponding to any particular epoch of the
earth’s magnetic field, is therefore proportional to the length
of that epoch. In the case of the shortest events detected
with certainty in the anomalies of the various ridges, this
width is of the order of 2 km or less on each side of the ridge,
approaching the limit helow which blocks would not he de-
tected on a magnetic profile.
If the new crust is formed by dyke injection, some mix-
ing of basalts of opposite polarity will take place unless the
volume between dykes from the same epoch is so small that