Rit (Vísindafélag Íslendinga) - 01.06.1967, Page 55

51
Icelandic basalts do show higher iron content and lower mag-
nesia than basalts from other parts of the Mid-Atlantic rift
zone. This holds also for the least differentiated members of
the tholeiitic series and it appears to be true for other basal-
tic areas in the northem Atlantic.
When compared to basalts dredged from various parts of
the Mid-Atlantic rift zone there appears to be a gradual
increase in iron content towards higher latitudes. The num-
ber of analysed samples from this large area is hardly suffi-
cient to allow any valid generalizations, but the present
data indicate either mantle inhomogeniety or different phy-
sical environment during magma generation on the north-
ern part of the Mid-Atlantic Ridge.
Some authors have suggested contamination by continental
material in order to explain the chemical differences between
the Icelandic basalts and basalt from other parts of the Mid-
Atlantic rift zone. It does however seem rather difficult to
visualize any continental material, which added to a “pri-
mary” basaltic liquid could give rise to the chemistry of the
Icelandic basalts.
DISCUSSION
Trausti Einarsson: From a physical point of view I find
the hypothesis of partial melting and filter pressing as the
origin of basaltic magma very difficult to accept. The fluid
part would be 108—1012 times as viscous as water. How can
such a fluid be pressed through a filter of residual crystals
without destroying it and carrying it along? I prefer to think
in terms of different depths of origin of the different funda-
mental types of basalt, and to explain differences in depth
on a mechanical basis. In some cases the stresses are great
and the fractures statistically deep and a corresponding type
of magma is favoured; in other cases there are weaker stres-
ses, shallower fractures, and another type of magma. The
connection between depth of earthquakes foci and magma