Jökull - 01.12.1984, Page 85

Profile Av. altitude Av. thickness Number of
dykes
Snið Meðalhæð Meðalþykkt Fjöldi ganga
(m) (m)
1 0 3.2 40
2 0 4.8 20
3 100 3.0 37
4 50 4.4 14
5 150 4.8 21
6 100 4.2 20
7 200 3.9 23
8 150 6.3 4
9 300 5.5 26
10 100 4.6 32
11 150 5.3 21
12 0 3.6 26
13 250 4.6 25
14 500 2.2 13
15 150 4.8 40
TABLE 1. Average altitude of the fifteen profiles in northwestern Iceland, and the average thickness,
and the number of, dykes in these profiles.
TAFLA 1. Meðalhœð sniðanna fimmtán yfir sjó, og meðalþykkt og fjöldi ganga í sniðunum.
logy of dykes and lavas; (4) vesicles and amyg-
dales in dykes and lavas; (5) site of dyke intru-
sion; that is, does the dyke occupy a fault? (6)
columnar jointing in dykes and lavas; (7) dyke
shape; and (8) how the dykes end laterally and/or
vertically. Furthermore, strike, dip and throw of
all faults in the profiles was measured wherever
possible.
Dip and strike were measured with a compass,
and the dyke thickness was measured with a tape.
Fault throw was measured either directly with a
tape or estimated by hand leveling. Accuracy in
measurements is 0.5 m for dyke thickness and
fault throw, and it is 2° for strike.
Each dyke observed in the field was located on
an air photograph. For an interval chosen at will
on the air photographs, it was therefore possible
to calculate the number of dykes, their cumula-
tive thickness and the corresponding dilation.
DYKES
Dip and strike
Most of the dykes are subvertical and cut the
lavas at nearly right angles. Figs. 3 and 4 show the
dip distribution for north or south and east or
west dipping dykes respectively. About 50% of
the dykes dip to north, and about 94% of the
dykes dip within 10° of the vertical. As most lavas
dip to south, about 5°, this indicates that initially
most of the dykes were vertical. Along profile 10
Fig. 3. Dip distribution of 275 dykes in NW-Ice-
land. These dykes dip to north or south. About
93% have dips within 10° of the vertical.
Mynd 3. Halli 275 ganga sem halla til norðurs eða
suðurs.
JÖKULL 34. ÁR 83