Jökull - 01.12.1994, Side 9

NNE-SSW north and east of it. Dykes in the research
area are few and they trend NE-SW.
Secondary mineral assemblages of the lava suc-
cession were classified according to Walker (1960).
The alteration stage of the lava pile in Isafjarðardjúp
is low and the basalt flows are relatively fresh. Fig. 9
shows a transection of the mapped area and the zeo-
lite zones. In the westem part of the area the topmost
zone, the zeolite-free zone, can in places reach 600 m
thickness which is unusual. The underlying chabazite
zone which is exposed in Alftafjörður, is missing in
Skötufjörður and Hestfjörður but appears again in
Mjóifjörður. The reason for the rise in the upper limit
of the chabazite zone at both ends of the section is
presumably their closeness to the down-dip Alfta-
fjörður central volcano to the west and the Reiphóls-
fjöll central volcano to the southeast.
PALEOMAGNETISM
Previous work
Kristjánsson (1968) carried out a preliminary pa-
leomagnetic survey on a few short profiles to the west
of Álftafjörður. Kristjánsson et al. (1975) sampled a
400-m lava profile in Arnarfjörður. This sampling
was greatly expanded in the 1975-78 collection by
McDougall et al. (1984) of cores from 1261 flows in
composite sections on the west, south and east coasts
of the peninsula. No paleomagnetic measurements
have been made previously on samples from the area
between profiles DO and DM, nor has any sampling
for such work been done so far on the northeastem
side of Isafjarðardjúp.
Sampling and measurements
Paleomagnetic core samples of 24-25 mm diame-
ter were collected using a portable gasoline-powered
drill, in 1982-85. They were oriented by geographic or
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