Jökull - 01.12.1976, Page 29

„V -63* 30'
Fig. 4a. Magnetic field over Heimaey island
(1800 m) in 1964.
Mynd 4a. Segulsvið yfir Heimaey 1964, skv.
bandarislium meelingum.
covered during drilling. Such a log may also
yield information relating to other geological
questions.
Thermomagnetic measurements on deep-drill
chips (Kristjánsson 1972) show that they have
a Curie point of ^ 560° C, indicating that
their magnetic mineral is essentially pure
magnetite.
As the magnetic minerals in surface basalts
cover a wide range of Curie points (from less
than 100° C) it is apparent that upon burial
and heating in an oxidizing environment,
titanomagnetites that have been originally pre-
sent in the rock have been exsolved into magne-
tite and (probably) ilmenite. Previous measure-
ments on samples of drill chips from Reykjavík
and Reykjanes, indicated that their mean sus-
ceptibility is higher than that in local surface
Fig. 4b. Magnetic field over Heimaey along
profiles AA at 6000' (1800 m) and BB at 1000'
(300 m) in 1973.
Mynd 4b. Segulsvið á tveimur fluglínum yfir
Heimaey 1913.
Fig. 5. Susceptibility of six basalt samples at
room temperature, after heating to various tem-
peratures in air.
Mynd 5. Segullirifstuðlar sex blágrýtissýna eft-
ir upphitun.
JÖKULL 26. ÁR 27