Greinar (Vísindafélag Íslendinga) - 01.01.1977, Page 88

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that there could be recognized any significant difference. But the
available material turned out not to be good enough. The elear
and significant difference is now known (63). Moreover the time
order of the chemistry in an eruption has also been recognized
(64). The petrologist K. Grönvold has also kindly pointed out
to the author that the analyses by T. Tryggvason in 1943 (65)
do show such time order for the shieldvolcano Skjaldbreiður.
It was also discovered (66) that in trace elements, there is a
difference of shieldvolcano and fissure lavas in Iceland. Further
differentiation in basalts increases from a general low level
of K20 on submarine ridges, to a maximum in the Kverkfjöll
area, in about central Iceland (67, 68, 69), Fig. 12. The reason
for this increase in differentiation need not be farfetched, but
has been discussed by the quoted authors as evidence and even
proof of “the greatest Hot Spot on the earth”, a “hotspot”
meaning a mantle plume from the Low velocity layer of seis-
mology.
At a meeting of the Geoscience Society of Iceland, February
7th 1975, On Hot Spots, G. Sigvaldason presented the petro-
Fig. 12. Increase of K20 in basaltic lavas, from submarine ridges towards
the Kverkfjöll area in Iceland. (After (66)).