Jökull - 01.12.1984, Page 86

(Fig. 2) I tested whether a significant change in
dip of the dykes occurred. No such change was
found and neither was there any significant
change in dip of lavas along this same profile.
Fig. 5 shows strike distribution of the dykes.
About 57.5% of the dykes strike between N50°E
and E. Fig. 6 is a rose diagram of the dyke strike
in the main research areas and indicates that
there are at least three main dyke directions in
this part of northwestern Iceland. In the most
southern area most dykes strike nearly E, but NE
and NNE directions are common in the more
northern areas. Fig. 7 shows the poles to all dykes
in these areas. Clearly, the majority of the dykes
have an ENE trend.
Thickness
The average thickness of the dykes is about 4.3
Fig. 4. Dip distribution of 111 dykes in NW-Ice-
land. These dykes dip to east or west. About 95%
have dips within 10° of the vertical.
Mynd 4. Halli 111 ganga sem halla til austurs eða
vesturs.
m. Fig. 8 shows the thickness distribution.
Although the average thickness is over 4 m,
about 34% of the dykes are less than 2 m thick.
The average thickness of dykes in the fifteen
profiles (Fig. 2) is given in Table 1. The largest
average thickness, 6.3 m (profile 8), is based on
too few measurements to be significant. But the
second largest average thickness, 5.5 m (profile
9), is significantly larger than the smallest aver-
age thickness, 2.2 m (profile 14).
The thickness distribution of dykes in the fif-
teen profiles, shown in Fig. 9, is clearly variable.
For instance, the variation in thickness is large in
profiles 4, 10, 11, 12 and 15, but small in profiles
2, 3 and 14. Neither the average thickness nor the
thickness distribution can be related to the alti-
tude of the profiles (Table 1, Fig. 9), nor to their
location in the research areas (Fig. 2).
Fig. 5. Strike distribution of 402 dykes in
NW-Iceland. About 49% have an azimuth angle
between 60° and 90°.
Mynd 5. Strikstefna 402 ganga.
Fig. 6. Rose diagrams for
dykes in the main research
areas. The numbers refer to
the number of dykes mea-
sured in the enclosed areas.
Mynd 6. Stefnurósir ganga á
aðal rannsóknarsvœðunum.
84 JÖKULL 34. ÁR