Jökull - 01.12.1982, Síða 106

a large number of samples from geothermal drill
holes in order to find the effect of alteration on
magnetite content in basalts. Kristjansson (1975,
1976) has discussed some aspects of drill hole mea-
surements that are specific to Iceland.
Specific anomalies have been studied by Fridleifs-
son and Kristjansson (1972), Schönharting and Pedersen
(1978) and Schönharting (1979). Magnetic properties
ofdredge samples from offshore anomaly areas were
measured by de Boer (1975) and Kristjansson et al.
(1976, \911).Piper (1973c) also discussed thepossi-
ble eífect of large-scale remagnetization, by reheat-
ing and alteration, upon magnetic anomalies.
DISCUSSION
Paleomagnetic and rock magnetic research has
advanced on a great many fronts during the last 30
years, and it is difficult to say whether progress on
any particular aspect has been of more importance
to earth science in general than progress on other
aspects. However, it is clear that the paleomagnetic
research that was carried out on Icelandic rocks
during the fifties was instrumental in accelerating
the general acceptance of paleomagnetic results
(both regarding reversals and pole positions) as
meaningful indicators of global phenomena. The
methods and conclusions of this research have been
confirmed to be valid, and the above acceptance led
toa revival ofcontinental drift theories in thesixties.
W'ork on paleomagnetic polarities in Iceland has
since 1960 been very useful in local stratigraphy and
related studies such as paleoclimatology and tec-
tonics, and it has helped in establishing the geo-
magnetic polarity time scale, but has not had as
much influence on earth science in general as did
thc early work. This may be partly due to the fact
that accurate dating of Icelandic lava flows has
proved to be very difficult. Similarly, results from
Iceland on past geomagnetic secular variation, on
the petrology of magnetic minerals etc. have been
useful to other branches of geoscience research but
without having decisive influence on these.
Much work remains to be done on the paleo-
magnetism of Icelandic rocks: several large areas
are still uncharted, particularly those that are volc-
anically and tectonically disturbed or heterogene-
ous; sediments within and around the island have
only been measured to a very small extent; subsur-
face work (remanence in cores from deep drill holes)
has just begun; the magnetization of intrusions and
associated quantitative analysis of magnetic ano-
malies is also at a very preliminary stage; and cer-
tain alteration and stability problems in various
rock types need attention.
ACKNOWLEDGEMENTS
ProJ. Thorbjöm Sigurgeirsson, R. L. Wilson and Jan
Hospers provided much helpful information and constructive
commenlsJor thispaper.
REFERENCES
Ade-Hall, J. Al. 1964: Electron probe microanalyser
analyses of basaltic titanomagneties and their
significance to rock magnetism. Geophys. J.R.
Astr. Soc. 8:301-312.
Ade-Hall, J. M. 1969: Opaque petrology and the
stability of natural remanent magnetism in bas-
altic rocks. Geophys. J. R. Astr. Soc. 18:93-107.
Ade-Hall,J.M., R.L. Wilson and P.J. Smith 1965: The
petrology, curie points and natural magnetizat-
ions of basic lavas. Geophys. J. R. Astr. Soc. 9 :
323-336.
Ade-Hall,J. M., and E. A. Lawley 1970: An unsolved
problem - opaque petrological differences bet-
ween Tertiary basalt dykes and lavas. Geol. J.
Spec. Issue no. 2 : 217-230.
Ade-Hatl, J. M., H. C. Palmer and T. P. Hubbard
1971: The magnetic and opaque petrological
response of basalts to regional hydrothermal
alteration. Geophys. J. R. Astr. Soc. 24: 137-
174.
Angenheister, G., N. Petersen and G. Schönharling 1977:
Zur Interpretation der Anomalien des Erdmag-
netfeldes in Island. Fortschr. Mineral. 54 : 54-
92.
Becker, H. 1980: Magnetic anomalies (AZ) in NE-
Iceland and their interpretation based on rock-
magnetic investigations. J. Geophys. 47 : 43-56.
de Boer, J. 1975 : Variations of the magnetic pro-
perties of pillow lavas along the Reykjanes
Ridge. J. Geophys. Res. 80 : 3769-3776.
Bird, C. F., and j. D. A. Piper 1980: Opaque petro-
logy, magnetic polarity and thermomagnetic
properties in the Reydarfjördur dyke swarm,
Eastern Iceland. Jökull 30 : 34-42.
Bragason, H. 0. 1981: Paleomagnetic measurements
in Jökuldalur. B.Sc. (Hons.) thesis, University of
Iceland, 47 pp. (In Icelandic).
Brynjóljsson, A. 1956: Ergebnisse bei partieller Ent-
102 JÖKULL 32. ÁR