Greinar (Vísindafélag Íslendinga) - 01.01.1977, Side 11

9
ed by local glaciers creeping down from individual volcanic
tuffbreccia heaps during a spell of cold climate. It seems most
likely that during the regression at the end of the Eocene,
warm currents were prevented by emerging banks from reach-
ing Iceland. This would very naturally lead to a cold climate,
because the warm current of today keeps the coastal annual
temperature 10°C above the average for the 65° latitude. But
for the Gulf Stream, Iceland might now be entirely glaciated.
These ages relating to Iceland are of special importance for the
history of the North Atlantic. Furthermore, we now see clearly
that there has been no “spreading” in Iceland since the Eocene.
After realizing that the deeper seismic layers may go re-
gularly through a complex geological structure, we see that
the seismic layers must have been formed by some special pro-
cesses. As the Moho also ignores structure, a special process
must also be sought for its creation at various times. We pro-
pose a diminuation of crystals by shear processes and then
a change into a dense polymorph, which is then consistent
with a relatively low confining pressure. The Upper Mantle is
then for various reasons considered to be chemically close to
shieldvolcano and plateau basalts, but in a solid dense nano-
crystalline state. When the, atmospherically created, crustal
stress field is of such intensity that in a deep shear fracture
the strain is not elastic at a depth where magma temperatures
occur, but is instead turned into heat, the bonds connecting
the nanocrystals in the solid state give away, and the dense
crystals expaned into those in mineralogical equilibrium with
a basaltic melt. Thus a magma reservoir is created, until its
expansion opens the fracture from below and leads to an erup-
tion. Nanocrystals may possibly be found in the thick crust
of submarine pillows, formed at a greater depth than 2180 m
(critical pressure of water). That may be an explanation of
the fact that excess argon is just found in such crustal glass.
The so inferred possible existence of nanocrystals in available
material could be tested. A positive result would in any case
tell something about the formation of basaltic magma.
The Moho is considered to sink and the ocean floor corre-