Jökull - 01.12.1984, Blaðsíða 88

columns. The number of columnar rows in indi-
vidual dykes is from one to over twenty. As a
rule, only the thinnest dykes (a few tens of centi-
meters in thickness) have only a couple of rows.
The thicker dykes in general have three or more
columnar rows. Most of the inner columnar rows
of the dykes are without chilled edges.
In some of the lateral and vertical sections,
dykes are disconnected. In some other sections,
the parts of the dyke are connected by thin veins
(Fig. 11), in particular where the dykes dissect
scoria between the lava flows. Where the dykes
are laterally or vertically offset, some of them
gradate into palagonite tuff and breccia.
Eleven dykes were seen to end upwards. The
dykes end in different ways (Fig. 12), but most of
them simply taper away. Where the very ends of
the dykes could be observed, it could be demons-
trated that, except in one instance, no fractures
associated with the mechanical effects of the
intrusion occur ahead of the dykes. In one inst-
ance, however, the dyke has apparently given
rise to a few normal faults at its upper end (Fig.
13).
-r < M f ' 1 i ' " ...................... ■ ■ ■ ’ i
0 5 10 15 20 25
Thickness, m
15
74
13
12
11
10
9
8
7
6
5
4
3
2 Fig. 9. Thickness distribution
of dykes in the profiles 1 to
15. See location of the pro-
^ files in Fig. 2.
Mynd 9. Þykktardreifing
ganga í þeim 15 sniðum sem
sýnd eru á mynd 2.
86 JÖKULL 34. ÁR