Rit (Vísindafélag Íslendinga) - 01.06.1967, Page 39

35
Applying the above figures to the whole of Iceland, a cross-
section from E to W 500 km long and 1000 m high above
sea level, i.e. 500 km2, a total dyke thickness of 19 km would
he required to build the Icelandic lava pile presently above
sea level, thus extending the base of the lava pile 19 km by
dyke injection. Assuming total thickness of 10 km for the
basalt pile, 1000 m above sea level and 9 km below sea level,
the cross-sectional area for Iceland is 5000 km2 and requires
dykes with aggregate thickness of 200 km. Dyke injection
would then cause 200 km extension of the pile from E to W.
Bödvarsson and Walker assume 6000 km2 as the cross-sec-
tional area of Iceland from E to W and extension by dyke
injection and normal faults amounting to 250 km drift at the
base of the pile. Their interpretation of gravity and seismic
data is, briefly, a 3—4 km thick upper basalt layer resting on
a 10—20 km thick “blister” composed of basalt lavas and a
great number of dykes and other minor intrusions.
The over-all picture of Bödvarsson’s and Walker’s hypo-
thesis is that of a central volcanic belt active from Tertiary to
Recent, whose activity has resulted in a great deal of dyke
injection, wedging the east and west halves apart with time,
with younger rocks continually forming in the middle.
Trausti Einarsson (1965) discussed the above hypothesis
and based his criticism mainly on the following: If a statio-
nary N-S trending volcanic zone has been operative from
Tertiary to Recent as assumed by Bödvarsson and Walker,
the many dykes intruded into that zone would have led to
a gravity anomaly elongated in the direction of the volcanic
zone, roughly N-S. On the contrary the Icelandic gravity
field is oval shaped with its longest axis in an E-W direction
and has acquired its shape through block-faulting, which deli-
neates roughly the present outlines of the country.
In the opinion of the present writer Einarsson’s criticism
on this point is not entirely valid. If a great deal of drift in
an E-W direction is permitted the width of the total dyke
swarm could exceed the N—S length of the volcanic zone,